Arahan Teknik (Jalan) 13-87 - A Guide to the Design of Traffic Signal
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Arahan Teknik (Jalan) 13/87
A Guide to the Design of Traffic Signals
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Roads Branch Public Works Department Malaysia Jalan Sultan Salahuddin 50582 Kuala Lumpur
ARAHAN TEKNIK (JALAN) 13/87
JABATAN KERJA RAYA
CAWANGAN JALAN IBU PEJABAT J.K.R., JALAN SULTAN SALAHUDDIN 50582 KUALA LUMPUR.
HARGA : RM 12.00
Page 1
PREFACE
This Arahan Teknik (Jalan) on "A Guide to the Design of Traffic Signals" is to be used for the design of traffic signals at all intersections. It is to be used in conj unction with Arahan Teknik (Jalan) 11/87 s "A Guide to the Design of At - Grade intersections" and rather relevant Arahan Tekniks. This guideline presents fundamental concepts and practices related to traf fic signal design that are to be adopted. In the past, road engineers have been relying totally on the suppliers to come up with signal timings and location design. With this gp;ideline, it is hoped that road engineers will now be responsible for every aspcet of traf fic signal design instead of adopting the supplier's design. This Arahan Teknik vill be updated from time to time and in this respect, any feedback from users will be most welcome. Any comments should be sent to Cawangan Jalan, lbu Pejabat JKR, Malaysia.
Page 2
CONTENTS
CHAPTER I
CHAPTER 2
CHAPTER 3
CHAPTER 4
INTRODUCTION 1.1
OBJECTIVES OF TRAFFIC SIGNAL CONTROL
1.2
ADVANTAGES AND DISADVANTAGES OF SIGNAL CONTROL
SIGNAL INSTALLATION CRITERIA 2.1
GENERAL
2.2
WARRANT ANALYSIS
SIGNAL OPERATION REQUIREMENTS 3.1
PHASING ELEMENTS
3.2
RIGHT-TURN PHASING
3.3
SUGGESTED GUIDELINES FOR SEPARATE RIGHT-TURN PHASES
3.4
SELECTION OF PRETIMED OR ACTUATION SIGNAL
SIGNAL DISPLAY AND LOCATION 4.1
SIGNAL DISPLAY REQUIREMENTS
4.2
NUMBER AND LOCATION OF SIGNAL FACES
4.3
NUMBER OF LENSES PER SIGNAL FACE
4.4
SIGNAL SIZE, BACKPLATE, POST AND ARRANGEMENT
4.5
EQUIPMENT AND MATERIAL
4.6
FLASHING OPERATION OF TRAFFIC SIGNALS
4.7
SIGNAL MOUNTING ALTERNATIVES
Page 3
CHAPTER 5
CHAPTER 6
TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.1
GENERAL
5.2
PRETIMED CONTROLLERS
5.3
ACTUATED CONTROLLERS
5.4
CONTROLLER LOCATION
5.5
DETECTORS
5.6
LOCATION OF DETECTORS
5.7
INSTALLATION CONSIDERATIONS
TRAFFIC SIGNAL TIMING
6.1
OBJECTIVE
6.2
DESIGN PRINCIPLES 6.2.1 Determination of basic saturation flow, S 6.2.2 Determination of Y value 6.2.3 Determination of total lost time per cycle, L 6.2.4 Determination of optimum cycle time, Co 6.2.5 Determination of signal settings 6.2.6 Determination of Capacity 6.2.7 Determination of delays and queues
6.3
GUIDING PRINCIPLES
Page 4
CHAPTER 7
DESIGN OF PROGRESSIVE SIGNAL TIMING 7.1
ADVANTAGES
7.2
APPLICATIONS
7.3
PROGRESSIVE SIGNAL SYSTEM DESIGN
BIBLIOGRAPHY
GLOSSARY
APPENDIX A :
DESIGN EXAMPLE
APPENDIX B :
VEHICLE - ACTUATED SIGNAL FACILITIES
Page 5
LIST OF FIGURES
PAGE
FIGURE
2-1
Peak hour volume warrant-urban or low speed
2-2
Peak hour volume warrant-rural or high speed
3-1
Two phase cycle
3-2
Three phase cycle
3-3
Four phase cycle
3-4
Heaviest right turn protected (leading green)
3-5
Heaviest right turn protected (lagging green)
3-6
Both right turns protected - no overlap (lead dual right)
3-7
Both right turns protected - no overlap (lag dual right)
3-8
Both right turns protected with overlap (quad right passing)
3-9
Lead lag
3-1.0
Directional separation
4-1
Cone of Vision for two lane approach
4-2
Typical arrangements of lenses in signal faces
4-3
Signal head configuration
4-4
Simple two--pole span
4-5
Bast arum with one overhead and one side mount signal head
6-1
Traffic Signal Calculations Reserve Capacity Diagram
7-1
Typical time space diagram
Page 6
LIST OF TABLES
PAGE
TABLE
2-1
Vehicular Volume Requirements for Warrant 1
3-1
Comparison of Right-turn phase alternatives
4-1
Minimum Visibility distances
4-2
Adjustments for Grade Guidelines
5-1
Safe Stopping distance and detector setback
6-1
Relationship between effective lane width and saturation flow
6-2
Correction factor for the effect of gradient
6-3
Correction factor for the effect of turning radius
6-4
Correction factor for turning traffic
6-5
Conversion factors to P.C.U.'s
6-6
Tabulation of
A=
(I - X2) ----------2(1 - Xx)
6-7
Tabulation of
B=
X2 ---------2(1 - x)
6-8
Correction term of equation d = cA + B - K --q as a percentage of the first two terms
6-9
Level of Service for Signalised Intersection
6-10
Level of Service of Road
Page 7
Chapter 1 INTRODUCTION
1.1
OBJECTIVES OF TRAFFIC SIGNAL CONTROL The overall objective of signal control is to provide for a safe and efficient traffic flow through intersections, along routes and in road networks. At individual intersections, the primary purpose is to assign right-of-way for alternate roads or road approaches in order to maximise capacity, minimise delay and reduce conflicts. On a road system or network the overriding objective is to optimise the safety and efficiency of traffic flow on the system, which sometimes results in compromises at individual intersections.
1.2
ADVANTAGES AND DISADVANTAGES OF SIGNAL CONTROL Traffic control signals,properly located and operated may provide one or more of the following advantages: (a)
(b)
Provide orderly movement of traffic through an intersection. Minimise the number of conflicting movements
ARAHAN TEKNIK ( JALAN ) 13 / 87
(c)
Increase the traffic han dling capacity of the intersection.
(d)
Provide a means of interrupting heavy traffic to allow other traffic to enter or cross.
(e)
Can be coordinated to provide for nearly continuous movement of traffic at a desired speed along a given route.
(f)
Promote driver confidence by assigning right-of-way.
Traffic signal installation even though warranted by traffic conditions and properly or improperly located, designed, or operated, can produce the following d1sadvantages:(a)
Increase total intersection delay especially during off peak periods.
(b)
Probable increase in certain types of accidents (rear end collisions)
(c)
Can interrupt the progressive flow of traffic on a route causing increased delay and stopping. Page 8
INTRODUCTION
(d)
When improperly located causes unnecessary delay and promote disrespect for this type of control.
(e)
When improperly timed, causes excessive delay, increasing driver irritation.
(f)
In rural areas whore distinct peak hours traffic exist, serious accidents can occur during off-peak hours (eg. midnight) when some drivers on the major road may jump the red light.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 9
Chapter 2 : SIGNAL INSTALLATION CRITERIA 2.1
GENERAL A request. to install new traffic signals (or upgrading an existng signalised intersection) may originate from various sources. The most usual sources include : (a)
Responsible agencies ( e.g. JKR, City Hall, Municipalities etc. )
(b)
Traffic : Enforcement Agencies ( e.g. Police )
(c)
Industrial or commercial developers and operators
(d)
In general the following steps should be taken prior to the installation of traffic signal control:(a)
Determine the function of the intersection as it relates to the overall road system. A system of major roads should be designated to channel major flow from one section of the city to another. Intersection controls must be related to the major road system.
(b)
A comprehensive study of traffic data and physical characteristics of the location is necessary to determine the need for signal control and for the proper design and operation of the control.
(c)
Determine if the geometric or physical improvements or regulations will provide a better solution to the problem of safety or efficiency than the installation of signal control.
(d)
Use establised warrants to determine if intersection control is justified.
Media/General Public
From whatever source the request may originate the responsible agency must determine whether such requests are justified. It is for this purpose that the following criteria of selection were developed. These criteria should be viewed as guidelines, not as hard and fast values. Satisfaction of a criteria does not : guarantee that the signal is really needed. Conversely, the fact that a criteria is not fully satisfied does not constitute absolute assurance that signalisation would not serve a useful purpose. Awareness of local conditions and sound engineering judgement would make the guide lines more effective. ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL INSTALLATION CRITERIA
2.2
WARRANT ANALYSIS Generally the following warrants should be considered before installing any signal control. They are namely :(1)
Vehicular Operations
(2)
Pedestrian Safety (S)
(3)
Accident Experience
For the minor road, the higher volume approach (one direction only) is used. An "average" day is defined as a weekday representing volumes normally and repeatedly found at the location.
Traffic control signals should generally not be installed unless one or more of the warrants in this guideline are met.
Warrant 1 : Vehicular Operations (a)
Total Volume
Vehicular volume affects the efficiency and the Level of Service of an intersection. High traffic volume on the major road especially during peak hours, would invariably cause considerable delay for the traffic on the minor road . For the purpose of determining the need for signal control, both the traffic volumes on the major and minor roads should be considered. A signal control is warranted if the traffic volume for each of any 8 hour of an average day meets the minimum requirements in Table 2.1. For the major road, the total volume of both approaches is used. ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL INSTALLATION CRITERIA
Table 2-l Vehicular Volume Requirements for Warrant I
------------------------------------------------------------------------------------------------------Number of Lanes Minimum Requirements (PCU) Each Approach -----------------------------------------------Majur Road (1) Minor Road (2) ------------------------------------------------------------------------------------------------------Major Minor Urban Rural Urban Rural Road Road ------------------------------------------------------------------------------------------------------1 1 500 350 150 105 2 or more
1
600
420
150
105
2 or more
2 or more
600
420
200
140
1 2 or more 500 350 200 140 ------------------------------------------------------------------------------------------------------(l) (2)
Total volume of both approaches Higher volume approach only
(b)
Peak Hour Volume
Peak hour volumes could also he used to determine the need for sigomliaation. This is applied in cases where, for one peak boor of an average day, traffic conditions are such that the minor road traffic experiences undue delay or hazard in entering or crossing the major road. This criteria warrants aigoaIioatiuo when the peak hour major road volume (total vehicles per hour for both approaches) and the higher volume minor road approach (vehicles per hour for are direction only) fall ARAHAN TEKNIK ( JALAN ) 13 / 87
above the curve for a given combination of approach lanes shown in Figure 2. The requirements are lower when the 85 percentile speed of major roadtraffic exceeds 60 km/hr, or when the intersection lies within a rural area. The peak hour volume warrant is satisfied when the volumes referred to fall above the curve for the given combination of approach lanes shown in Figure 2.2.
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SIGNAL INSTALLATION CRITERIA
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL INSTALLATION CRITERIA
(c)
Progressive Movements
In some locations., it may be desirable to install a signal to maintain a proper grouping or platooning of vehicles and regulate group speed even though the intersection. does not satisfy other warrants for signalisation. Several advantages may accrue from this type of consideration. Moving the traffic in platoons at the desirable speed would reduce the number of stops and delays. Accident reduction may also be expected with reduction of stops and speeds. On a one-way road (or a road with predominantly unidirectional traffic), this warrant applies when the adjacent signals are so far apart that they do not provide the necessary vehicle platooning and speed control. On a two--way road, the warrant is satisfied when the adjacent signals do not provide the necessary degree of platooning and speed control and the proposed and adjacent signals could constitute a progressive signal system. A signal installation under this warrant should be based on the 85-percentile speed unless a traffic engineering study indicates that another speed is more appropriate.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Warrant 2 : Pedestrian Safety Signalisation of an intersection also promotes pedestrian safety. It is warranted for signalisation when, for each of any 8 hours of an average day the following traffic volume exists : (a)
On the major road, 600 or more vehicles per hour enter the intersection (total of both approaches): or where there is a raised median island 1.2 m or more in width, 1,000 or more vehicles per hour (total of both approaches) enter the intersection on the major road and
(b)
During the same 8 hours as in paragraph (a) there are 150 or more pedestrians per hour on the highest volume crosswalk crossing the major road.
When the 85-percentile speed of major road traffic exceeds 60 km/hr in either an urban or a rural area or when the intersection lies within the built-up area of an isolated community having a population of less than 10,000, the minimum pedestrian volume is 70 percent of the requirements above.
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SIGNAL INSTALLATION CRITERIA
A signal installed under this warrant at an isolated intersection should be of the traffic actuated type with push buttons for pedestrian crossing the main road. If such a signal. is installed at an intersection within a signal system, it should be equipped and operated with control devices which provide proper coordination. Special considerations should be given at schools where large number of children crosses a major road on the way to and from school. The requirement for school children to cross is based on the number of adequate gaps available in the vehicular traffic on the major road available. A signal may be installed to artificially create these gaps if other methods for improvements are not adequate.
Warrant 3 : Accident Experience Accident prone areas with accident types which are correctable by signal control warrants signalisation. This claim should be substantiated by accident records for a period of two to three years. The requirements are satisfied when :
ARAHAN TEKNIK ( JALAN ) 13 / 87
(a)
An adequate trial of less restrictive remedies with satisfactory observance and enforcement has failed to reduce the accident frequency.
(b)
There exist a record of five or more reported accidents in a year. These accidents should be of types susceptible to correction by traffic signal control.
(c)
There exist a volume of vehicular and pedestrian traffic not less than 80% of the requirements specified in warrants 1 and 2.
(d)
The signal installation will not seriously disrupt progressive traffic flow.
Any traffic signal installed solely on this warrant should be semi traffic-actuated {with control devices which provide proper coordination if installed at an intersection within a coordinated system} and normally should be fully trafficactuated if installed at an isolated intersection.
Page 15
Chapter 3 SIGNAL OPERATION REQUIREMENTS
After establishing that a signal is warranted at a particular location, the next major step involves determining the most appropriate method of control. Decisions to be made at this level includes : (a)
Determining what are the phasing requirements
(b)
Whether the signal should be pretimed or actuated.
3.1
PHASING ELEMENTS Definitions : (i)
A signal phase = part of the cycle length allocated to a traffic movement receiving the right of way simultaneously during one or more intervals.
(ii)
A traffic movement- a single vehicular movement, a single pedestrian movement, or a combination of vehicular and pedestrian movements.
(iii)
Cycle length = the sum of all traffic phases.
ARAHAN TEKNIK ( JALAN ) 13 / 87
There are a number of phasing options available. The simplest signal cycle is a two phase cycle, in which each road in turn receives a green indication while the cross-road receives a red indication. A phasing diagram for a twophase cycle is shown in Figure 3.1. Three and four phase cycles are also quite common where there are heavy turning movements. The purpose of such multiphase cycle is to prevent traffic conflicts by giving heavy right-turn movements separate signal indications. Figures 3.2 and 3.3 illustrates three and four-phase signal cycles.
Page 16
SIGNAL OPERATION REQUIREMENTS
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 17
SIGNAL OPERATION REQUIREMENTS
When right turning movements are heavy, protecting its movements are quite often essential to avoid unnecessary conflicts. The basic: sequences which accomodate rightturn movements include : (a)
Heaviest right turn protected This is a "lead right" in which the right-turning vehicles from only one approach are protected and move on an arrow indication preceding the opposite through movement; or a "lag right" when the protected right turn follows the through movement phase. See Figures 3.4 and 3.5.
(b)
Both right turn protected-no overlap. When the opposing right turns move simultaneously followed by the through movements, it is termed "lead dual right". If the right turns follow the through movement it is called a "lag dual right". See Figures 3.6 and 3.7.
(c)
Both right turns protected-with overlap. In this operation, opposing right turns start simultaneously. When one terminates, the through movement in the same directions as the extending right. movement is started. When the extending right is terminated, the remaining through movement is started. When this type phasing is used on both roads, it is termed "quad right phasing". See Figure 3.8.
ARAHAN TEKNIK ( JALAN ) 13 / 87
(d)
Lead lag - This phasing is combined with a leading protected right in one direction, followed by the through movements, followed by a lag right in the opposing direction. It is sometimes used in systems to provide a wider two-way through band. See Figure 3.9.
(e)
Directional separation - First one approach moves with all opposing traffic stopped, then the other approach moves with the first approach stopped. See Figure 3.10.
( The signal displays shown in Figures 3.4 to 3.10 are those visible to the starred ( * ) right turn movement ).
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SIGNAL OPERATION REQUIREMENTS
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SIGNAL OPERATION REQUIREMENTS
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SIGNAL OPERATION REQUIREMENTS
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SIGNAL OPERATION REQUIREMENTS
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SIGNAL OPERATION REQUIREMENTS
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Page 23
SIGNAL OPERATION REQUIREMENTS
Although there are no limitations on the numbers of phases that can be utilized, as a general rule they should be held to a minimum, especially in pretimed controllers. More than three phases tend to increase the cycle length and delay as they reduce the green time available to the other phases and intersection efficiency is impaired by starting delays, additional change intervals, longer cycles, and so forth. Multiphase actuated controllers when properly operated and timed tend to reduce these undesirable effects. In determining the number of phases required at an intersection, the goals of safety and capacity may conflict. For example, in many situations protected right-turn phases are safe for right--turning vehicles than permissive right turns. However, the added phases may result in longer cycle lengths, reduced pro gression in systems, and increased delay and percent of vehicles stopped. These factors adversely affect traffic performance, capacity, and fuel consumption, and may tend to reduce safety for all traffic.
ARAHAN TEKNIK ( JALAN ) 13 / 87
3.2
RIGHT-TURN PHASING In general the phasing issue is primarily a rightturn issue. When right-turning volumes and. opposing through volumes increases, a point is reached where right-turning traffic cannot find safe and adequate gaps. The provision of separate right-turn lanes will minimize the problem somewhat by providing storage space for those waiting for an acceptable gap in opposing traffic to turn. If the problem persists, the decision to provide separate right-turn phasing should be carefully weighed. Two common right-turn phasing alternatives are the lead right and the lag right. -
Lead right : the protected right turn precedes the accompanying through movement.
-
lag right : the right turn phasing follows the through movement.
The most common practise is to allow opposing right turns to move simultaneously. This operation generally requires separate right-turn storage lanes.
Page 24
SIGNAL OPERATION REQUIREMENTS
In actuated control, it is frequently desirable to split the right-turn phase so that when the demand on one right-turn phase ceases, the opposing through movement is released. This works very well with lead-right operations. In lag right, it is usually desirable for the right turns to operate simultaneously. Both sequences have advantages and disadvantages as summarised in Table 3.1.
3.3
SUGGFSTED GUIDELINES FOR SEPARATE RIGHTTURN PHASES
Right-turn peak period volumes greater than two vehicles per cycle per approach still waiting at the end of green.
(b)
Minimum right-turn volumes of. greater than two per cycle during the peak period, and the average delay per right turning vehicle greater than 35 seconds.
(c)
The following suggested guidelines may be applied when considering the addition of separate right-turn phasing for intersections having an exclusive rightturn lane. (a)
Accident experience Four right-turn accidents in one year or six in two years for one approach. Six right-turn accidents in one year or ten in two years for both approaches.
Volume The product of rightturning vehicles and conflicting through vehicles during the peak hour is greater than 100,000 on a four-lane road or 50,000 on a two-lane road.
Delay
(d)
Geometrics Two or more exclusive right-turn lanes are necessary.
Right--turn volumes greater than 100 vehicles during the peak hour.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 25
SIGNAL OPERATION REQUIREMENTS
TABLE 3.1
Comparison of Right-Turn Phase Alternatives ------------------------------------------------------------------------------------------------------Lead Right-Turn Phase ------------------------------------------------------------------------------------------------------Advantages Disadvantages ------------------------------------------------------------------------------------------------------Iucreamem intersection capacity Right turns may preempt the on one or two-lane approaches right of way from the opposwithout right-turn lanes when ing through movement when compared with two-phase traffic the green is exhibited to the signal operation. stopped opposing movement. Minimizes conflicts between right-turn and opposing straight through vehicles by clearing the right-turn vehicles through the intersection first.
Opposing movements may make a false start in an attempt to move with the leading green vehicle movement.
Drivers tend to react quicker than with lag right operations. ------------------------------------------------------------------------------------------------------Lag-Right Turn Phase ------------------------------------------------------------------------------------------------------Both directions of straight through Right-turning vehicles can be traffic start at the same time. trapped during the right-turn yellow change interval as Approximates the normal driving the through traffic is not behavior of vehicle operators stopping as expected. Provides for vehicle/pedestrian separation as pedestrian usually crosses at the beginning of straight through green.
Creates conflicts for opposing right turns at start of lag start of lag interval as opposing right-turn drivers expected both movements to atom at the same time.
Where pedestrian signals are used, pedestrians have cleared the intersection by the beginning of the lag green interval.
Where there is no right turn lane, an obstruction to the through movement during the initial green interval is created
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL OPERATION REQUIREMENTS
------------------------------------------------------------------------------------------------------Lag-Right Turn Phase ------------------------------------------------------------------------------------------------------Cuts off only the platoon stragglers The hazards inherent in lagfrom adjacent interconnected interright operations are such that section. they tend to restrict its use to pretimed operations or to a few specific situations in actuated or control, such as "T' intersections. A green arrow cannot be displayed during the circular yellow, there fore, a stop-start sitnation is necessary with simultaneously opposing right turns.
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SIGNAL OPERATION REQUIREMENTS
3.4
SELECTION OF PRETIMED OR ACTUATION SIGNAL
(b)
3.4.1 Pretimed or Fix Timed Signal :This type of signal directs traffic to stop and permits it to proceed in accordance with a single, predetermined time schedule or a series of such schedules. The traffic signal is set to repeat a given sequence of signal indications regularly.
Can cause excessive delay to vehicles and pedestrians during. offpeak periods
3.4.2 Traffic Actuated Signals The operation of this type of signal is varied in accordance with the demands of traffic as registered by the actuation of vehicle or pedestrian detectors as one or more approaches.
Advantages of Pretimed Signals.
Advantages of Traffic Actuated Signals.
(a)
(a)
Usually reduce delay (if properly timed)
(b)
Adaptable to short-term fluctuations
(c)
Usually increase capacity (by reapportioning green time).
(d)
Provide continuous operation under low volume conditions as an added safety feature, when pretimed signals should be put on flashing to prevent excessive delay.
(e)
Especially effective at multiple phase intersections
(b)
Simplicity of equipment provides relatively easy servicing and maintenance. Can be coordinated to provide continuous flow of traffic at a given speed along a particular route, thus providing positive speed control.
(c)
Timing is easily adjusted in the field.
(d)
Under certain conditions can be programmed to handle peak conditions.
Disadvantages of Pretimed Signals. (a)
Do not recognize or accommodate shortterm fluctuations in traffic demand.
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SIGNAL OPERATION REQUIREMENTS
Disadvantages of Traffic Actuated Signals (a)
The cost of an actuated installations is two to five times the cost of a pretimed signal installation.
(b)
Actuated controllers and detectors are much more complicated than pretimed controllers, increasing maintenance and inspection skill requirements and costs.
(c)
Detectors are costly to install and require carefull inspection and maintenance to ensure proper operation.
3.4.3 Traffic-adjusted system These are centrally controlled, as, for example, by a digital computer, and have settings which are updated from measurements of the system through detectors.
3.4.4 Comparison of Pre-timed and Traffic Actuated Control With basic pre-timed control, a consistent and regularly repeated sequence of signal indications is given to traffic. By use of attached auxiliary devices or remotely located supervisory equipment, the operation of pre-timed control ARAHAN TEKNIK ( JALAN ) 13 / 87
can be changed within certain limits to meet the requirements of traffic more precisely. Pre-timed control is best suited to intersections where traffic patterns are relatively stable or where the variations in traffic flow that do occur can be accommodated by a pretimed schedule without causing unreasonable delay or congestion. Pre-timed control is particularly adaptable to intersections where it is desired to coordinate operation of signals with existng or planned signal installations at nearby intersection on the same road or adjacent roads.
Traffic-actuated control differs basically from pre-timed control in that signal indication are not of fixed length, but are determined by and confirmed within certain limits to the changing traffic flow as registered by various forms of vehicle and pedestrian detectors. The length of cycle and the sequence of intervals,may vary from cycle to cycle, depending on the type of controller and auxiliary equipment utilized to fit the needs of the intersection. In some cases, certain intervals may be omitted when there is no actuation or demand from waiting vehicles or pedestrians.
Page 29
CHAPTER 4 SIGNAL DISPLAY AND LOCATION
To serve its intended purpose in directing and regulating traffic flow, two fundamental principles must be carefully considered, i.e. conspicuity and clarity. Conspicuity means that the signal must not only be visible, but must be obvious to the eye and attract attention. Clarity means that the message or direction given can be easily understood. In other words, the signal must be seen in order for the driver to react and the required action must be obvious.
4.1
SIGNAL DISPLAY REQUIREMENTS For the driver to respond effectively to the traffic signal, these basic requirements has to be considered.
The amount of light reaching the driver's eye.
The position of the signal in the driver's field of view.
The ratio of the signalto-background contrast.
The amount of competing information sources (visual clutter or "noise")
ARAHAN TEKNIK ( JALAN ) 13 / 87
The degree to which the appearance -of the signal is expected.
The degree to which the precise location of the signal is known.
The degree to which the message conform to the driver's knowledge and expectations.
The physical details of these elements that ,feet the driver's ability to see and respond to message transmitted are provided below:
Minimum Visibility Requirements : Minimum visibility for a traffic signal is defined as the distance from the stop line at which a signal should be continuously visible for various approach speeds. Table 4.1 shows, for example, that if the 85percentile approach speed is 56 kph the signal faces should be visible from a distance of 99 m. And they should be continuously visible from that point all the way to the stop line at the intersection.
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SIGNAL DISPLAY AND LOCATION
As these distances do not consider the impact of grade, it may be necessary to adjust the minimum visibility distances to reflect an upgrade or downgrade approach. Table 4.2 can be used for this purpose. If the signal faces are not visible from the distance specified by the chart, signs WD.22 and WD.17 must be installed to warn drivers. (Please refer to "Arahan Teknik (Jalan) 2A/85 Manual on Traffic Control Devices : Standard Traffic Signs" for the details of the signs)
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SIGNAL DISPLAY AND LOCATION
Table 4.1 Minimum Visibility Distances 85 percentile speed, kph
Minumum Visibility Distance, m
Desirable Distance, m
32 40 48 56 64 72 80 88 97
53 66 82 99 119 140 165 190 218
81 99 123 146 174 201 232 265 299
Table 4.2 Adjustments for Grade Guidelines
85 percentile speed, kph Add for Downgrade, m
32 40 48 56 64 72 80 88 97
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Subtract for Upgrade, m
5%
10%
5%
10%
2 3 5 6 9 12 15 18 21
5 6 9 14 20 27 37 46 58
2 3 3 5 6 9 11 14 17
3 5 6 8 11 15 20 24 29
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SIGNAL DISPLAY AND LOCATION
4.2
NUMBER AND LOCATION OF SIGNAL FACES It is advisable that there be at least two signal indications for each through approach to an intersection or other signalised location. A single indication is permitted for control of an exclusive turn lane provided that this single indication is in addition to the minimum two for through movement lanes. Supplemental signal indications are recommended if their use will improve what would otherwise be marginal visibility or detectability of the signal indication. Additional heads used for this purpose should be located as close as possible to the driver's projected line of sight. Typical situations where supplemental indications may materially improve visibility include :
Approach widths in excess of three full lanes and very wide intersecting road.
Driver uncertainty concerning the proper location at which to stop.
High percentages of large trucks in the traffic stream that tend to block the view of signal indications in their normal location.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Approach alignment that makes continuous visibility of normally positioned signals impossible.
The placement of the signal face depends on the visibility requirements for a specific location. Generally, the precise location should consider the lateral and vertical angles of sight toward the signal as determined by (1) typical driver eye position; (2) vehicle design; and (3) the vertical, longitudinal, and lateral position of the signal face. The first two factors are relatively consistent. It is the third factor that varies as a function of the intersection geometry. Accordingly, the optimum physical layout of the individual intersection must be carefully designed to assure that the signal indication lies within the driver's cone of vision.
4.2.1 Cone of Vision Vertically, a driver's vision is limited by the top of the vehicle's windscreen. This restriction requires that the signal be located far enough beyond the stop bar to be seen by the driver of a stopped vehicle. The lateral location of the face is based on the driver's cone of vision and the width of the intersecting cross roads.
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SIGNAL DISPLAY AND LOCATION
It has been determined by recognized human factor studies that generally a driver's lateral vision is excellent up to 5 on either side of the center line of the eye position (a cone of 10 ). Vision is still very good up to 10 on either side (cone of 20 ). At 20 on either side (cone of 40 ), the driver's vision is judged as "adequate". Therefore it requires that at least one (and preferably two) signal faces be located within a cone 20 to the left or 20 to the right of the "center of the approach lanes extended." This constitutes the maximum acceptable cone. The cone of vision originates at a point which represents the center of the approach lanes at the stop line. Parking lane is usually excluded and separate turn lanes are included unless they are controlled by separate signal displays.
4.2.2 Lateral Clearance On roadways whose edges are defined by a raised kerb, the poles shall be erected so that no part of the signal head other than overhead signals project over the roadway. If possible the signal housing should have a clearance of a minimum 450 mm from the kerb line.
4.2.3 Height of Signal Faces The bottom of the housing of a signal face, not mounted over a roadway, shall not be less than 2.0 m nor more than 3.5 m above the sidewalk or, if none, above the pavement surface at the center of the roadway. The bottom of the housing of a signal face suspended over a roadway shall not be less than 5.5 m nor more than 8.5 m above the pavement surface at the center of the roadway.
This concept is illustrated in Figure 4.1. The maximum cone of vision in this figure is shown superimposed on a typical two-lane approach.
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
4.2.4 Other Locational Criteria : a)
4.3
Where a signal face is meant to control a specific lane or lanes of approach, its position should be unmistakably in line with the path of that movement.
b)
Where possible, signal displays which control through traffic must be located within a maximum of 35 metres beyond the stopline.
c)
Where the secondary signal face is more than 35 m and less than 45 m beyond the stop line, a supplemental near-side signal indications is required.
4.4
SIGNAL SIZE, BACKPLATE, POST AND ARRANGEMENT a.
For uniformity, only one standard size of signal indication is used i.e. the 300 mm lens. This 300 mm lens yields a maximum center luminance two or more times higher than the maximum center luminance of 210 mm indications. In addition, this larger size lens increases light output and provides better visibility.
b.
All these signal indications must be mounted on a black backplate with an orange colored border.
c.
The post must be colored in black and orange strips with a 0.3m interval (See Arahan Teknik Jalan 2B/85 - Traffic Sign Applications)
d.
Visors should be used in all installations.
e.
For typical arrangements, see Figure 4.2.
NUMBER OF LENSES PER SIGNAL FACE Each signal face, except in pedestrian signals, shall have at least three lenses, but not more than six. The lenses shall be red, yellow or green in color, and shall be given a circular or arrow type of indication. Allowably exception to the above is were a single section green arrow lens is used alone to indicate a continuous movement.
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
4.5
EQUIPMENT AND MATERIAL All equipments and materials must conform to BS 505 "Specification for Road Traffic Signals". The color of the light transmitted by the signals shall comply with the limits set out in British Standard 1376.
4.6
FLASHING OPERATION OF TRAFFIC SIGNALS All traffic signal installations shall be provided with an electrical flashing mechanism. A manual switch, or where appropriate, automatic means shall be provided to operate this.
Automatic changes from flashing to stop-and-go operation shall be made at the beginning of the major road green interval, preferably at the beginning of the common major road green interval, (i.e., when a green indication is shown in both direction on the major road). Automatic changes from stop-and-go to flashing operation shall be made at Lhe end of the common major road red interval, (i.e., when a red indication is shown both directions on the major road).
The illuminating element in a flashing signal shall be flashed continuously at a rate of not less than 76 nor more than 84 times per minute. The illuminated period of each flash shall be not less than half and not more than twothirds of the total flash cycle. When traffic control signals are put on flashing operation, the following meanings imply, (a)
The system breaks down or
(b)
Low-traffic period control (usually after midnight)
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
Where there is no common major road green interval, the automatic change from flashing to stop-and-go operation shall be made at the beginning of the green interval for the major traffic movement on the major road. It may be necessary to provide a short, steady all red interval for the other approaches before changing from flashing yellow to green on the major approach.
4.7
SIGNAL MOUNTING ALTERNATIVES There are three basic ways that signal indication may be mounted : 1.
post or pole mounted
2.
span-wire mounted
3.
mast-arm mounted
All post or pole mounted signals must be installed 2.0 m to 3.5 m above the sidewalk or pavement surface at the centre of the highway if no sidewalks exist. Typical post mounted signal installations are shown in Figure 4.3. Advantages-of Post-Mounted Signals are :
Low installation costs
Easy maintenance, no roadway interference
Generally considered as most aesthetically acceptable.
Generally good locations for pedestrian signals and push buttons.
The type of mounting used depends to some extend on local practice, aesthetic appearance and cost.
4.7.1 Post-or pole mounted signals The term post-mounted signals usually refers to signal head assemblies mounted on their own - 100 mm to 150 mm dia. metal post. Signals may also be mounted on poles used for other purposes (eg. lighting poles or telephone). ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
Where wide medians with right-turn lanes and phasing exist, provide good visibility.
Disadvantages are :
Advantages of two-pole simple span
Low installation-costs.
Allows good lateral placement of signals for maximum conspicuity.
Minimum number of poles to clutter sidewalk area
Easy to install, little or no underground work required.
May be combine'd with utility poles.
Requires underground wiring which may offset initial cost advantages May not provide locations which meet minimum conspicuity
Generally does not provide good conspicuity.
May not provide mounting locations such that a display with clear meaning is provided.
Height limitations may provide problems where approach is on a vertical curve.
4.7.2 Span-wire mounted signals : In a span-wire installation, all or most of the traffic signal faces are mounted overhead. In this application, strain poles are installed at two or more locations at the intersection, a messenger (or support) cable is strung between the poles, and signal heads are attached along the messenger. Wiring is run overhead.along the messenger cable to the signal heads. Figure 4.4 illustrates a simple span wire mounted signals. ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
ARAHAN TEKNIK ( JALAN ) 13 / 87
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SIGNAL DISPLAY AND LOCATION
Disadvantages of two-pole simple span
Advantages of Mast-Arm
Poor visibility from stop line at intersections of narrow streets.
Allows excellent lateral placement
Provides good conspicuity from stop-line
May result in very long spans.
May provide sidemount locations for supplementary signals or pedestrian faces and push buttons.
Generally accepted as an aesthetically pleasing overhead mounting.
Rigid mountings provide positive control of signal movement in wind.
All heads are located on one span maximizing loading on cable and poles. Often considered unpleasing aesthetically because of head "clutter".
Poor pedestrian visibility of indications.
No provision for serving all corners with pedestrian push buttons.
Disadvantages of Mast-Arm
Costs are higher than other mounting alternatives
On very wide approaches it may be difficult to properly place signal faces over the lanes they control.
4.7.3 Mast-Arm Mounted Signals Mast-arm mounting is a cantilevered structure which permits the overhead installation of the signal faces without overhead messenger cables and signal wiring. The cable connecting the signal heads to the controller is run inside the pipe and arm structure. The mast-arm mounting can be effectively combined with pole-mounted signals. Example of mast-arm installations is given in Fig. 4.5.
ARAHAN TEKNIK ( JALAN ) 13 / 87
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Chapter 5 TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
The designer should decide on the types of control he/she wants in the traffic system. The types of signal system controls have been discussed in Chapter 3. In the case of vehicle actuation control, the designer has to further decide on the type and location of the vehicle detectors required. It is proposed that all signal installations should be of the vehicle actuated control type.
5.1
GENERAL Traffic signal controller can be classified into either pretimed or actuated. Semi-actuated, full actuated, and volume-density modes can be provided within the current state-of-the art basic actuated controller unit.
5.2
PRETIMED CONTROLLERS This common type of controller operates according to a predetermined cycle lengths and phase intervals. It is frequently used when there are predictable and stable traffic volumes. It provides a simple, economical means of traffic control, and because of its simplicity, it is very reliable and relatively easy to maintain. Because pretimed control does not recognise or
ARAHAN TEKNIK ( JALAN ) 13 / 87
accommodate short-term fluctuations in traffic demand, it can cause excessive delay to vehicles and pedestrians where there exists a high degree of variability in the traffic flows.
5.2.1 Timing Characteristic : Pretimed controllers has the following characteristics from a timing standpoint : (a)
Provide a fixed amount of time for each phase interval
(b)
Each phase or movement can be divided into a number of discretely timed interval such as phase green, flashing walk, yellow change and all red clearance. The same timing is provided for each of these intervals regardless of demand.
Pretimed controllers do have a degree of flexibility in varying timing. Changes in timing can be accomplished to provide different, cycle lengths, interval timing, and/or offset. Timing plans are usually selected on a time-ofday/dayof-week basis by means of time clocks. Page 44
TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.3
ACTUATED CONTROLLERS A traffic-actuated controller operates with variable vehicular and pedestrian timing and phasing intervals which depend on traffic volumes or the presence of pedestrians. The flows are determined by vehicular detectors placed in the roadway or by pedestrian actuation of push buttons. The basic applications of actuated control include semi-actuated, full-actuated, and volume density.
5.3.1
SEMI-ACTUATED CONTROLLERS These devices provide the mean for traffic actuation on one or more, but not all of the intersection approaches. It is applicable primarily to an intersection of a heavy - volume, urban or suburban traffic arterial with a relatively lightly travelled minor road. The essential operating features of the controller are : a)
Detectors are on minor approaches only.
b)
Major, road receives a minimum green period in each cycle.
c)
Major road receives green indefinitely after minimum period, until interrupted by the minor phase detector, actuation.
ARAHAN TEKNIK ( JALAN ) 13 / 87
d)
Minor phase receives green after actuation provided major phase has completed minimum green period.
e)
Minor phase receives minimum initial green period.
f)
Minor phase green is extended by additional actuations until preset maximum limit is reached or a gap in actuations greater than the unit extensions occur.
g)
Additional actuation will be remembered if maximum has been reached on minor phase and will return green after major phase interval.
h)
Yellow change and allred clearance intervals are preset for each phase.
This kind of control is excellent for use where a light sideroad volume cannot safely cross major flows without signalisation. If sideroad flows are sporadic, the regular interruption of the major flow with pre-timed control cannot be justified. Where both road volumes fluctuate widely, semiactuated control should not be used, since there are no detectors on one or more legs. Page 45
TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.3.2 Full - Actuated Controllers This provides for actuation by vehicles on all legs of the intersection. It is applicable primarily to an isolated intersection of roads that carry approximately equal traffic volumes, but. where distribution between approaches varies and fluctuates. It then becomes necessary to take into consideration the demands on all approaches. The essential operating features of the controller are : a)
f)
Each phase has a recall switch -
when both recall switches are off the green will remain on one phase when no demand is indicated on the other phase.
-
when one recall switch is on, the green will revert to that phase at every opportunity.
-
when both recall switches are on, the controller will cycle on a fixedtime basis in the absence of demand on either phase (ore initial interval and one vehicle interval on each phase).
Detectors on all approaches
b)
Each phase has preset initial interval to provide starting time for standing vehicles.
c)
Green interval is extended by a preset unit extension for each actuation after the initial interval expires, provided a gap greater than the unit extension does not occur.
d)
Green extension is limited by a preset. maximum limit (some equipment can provide two maximums per phase).
e)
Yellow change and allred clearance intervals are preset for each phase.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Because of their actuated nature, full-actuated controllers cannot be coordinated with other signals without losing the flexibility for which they were designed. Demand patterns for which they are applicable, as well as the inability to coordinate make the requirements of isolated locations (about 2 km between adjacent signals) a fairly strong one.
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TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.3.3 Volume - Density Controllers This class of device offers additional responsiveness in signalisation for isolated intersections. Green time is allotted on the basis of volumes on approach legs. Unlike simple actuated signal, the volume-density signals does not merely react in a predetermined fashion to an actuation, but is able to record and retain information regarding volume, queue length, and delay times. In addition, a phase will lose the green by any one of three mechanism. a)
flexibility in traffic-actuated controllers, in that it is capable of taking into consideration the number of vehicles waiting on an approach, as well as the volume on the approach with the green indication. Its use is primarily applicable to an isolated intersection with wide traffic fluctuations between roads. The essential operating features of the controller are : a)
Detectors on all approaches
b)
Each volume density phase has an initial green time that, can be varied by :
There are no vehicles producing any further demand on the approach.
-
added initial,
b)
The maximum green phase is reached.
-
computed initial, or
c)
The time gap between vehicles on the approach exceeds the maximum standard.
-
extensible initial,
The last mechanism is the "density" function of the signal. At the beginning of a green phase, the maximum time gap might be, for example, 5 seconds. As the green phase continues, the maximum time gap decreases. The phase is lost when the maximum gap is exceeded, or when the maximum length of phase is reached, whichever comes first. This type of control provides the greatest ARAHAN TEKNIK ( JALAN ) 13 / 87
c)
Passage time is the extended green time created by each additional actuation after the initial green time has elapsed. This time is set as that required to travel from the detector to the stop line.
d)
Passage time is reduced to a minimum gap after a preset time.
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TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.4
e)
Maximum green or extension limits are preset for each phase.
f)
Yellow change and allred clearance intervals are preset for each phase.
CONTROLLER LOCATION
The signal controller may be attached to any convenient pole or, if a console cabinet is used, it may be placed wherever desired, provided that ,in either case the location chosen satisfies the following :(a)
A power supply can be conveniently obtained.
(b)
There will be an unobstructed view of all approaches to the intersecton in the event of manual operation. When this condition cannot be satisfied and manual operation is frequently required, it may be desirable to install a special remote unit at a more favourable position with its switches in parallel with those of the controller proper.
(c)
The cabinet does not unduly obstruct the pedestrian right of way.
ARAHAN TEKNIK ( JALAN ) 13 / 87
(d)
5.5
The cabinet will not be unduly exposed to accidental damage caused by passing traffic.
DETECTORS Traffic detectors are a primary requisite of actuated signal controls as they sense vehicular or pedestrian demand and relay these data to the local intersection controller or master controller so that the appropriate signal indications may be displayed. The selection of the type, design, and installation of the various types of detectors is a function of the operational requirements and physical layout of the area to be detectorised. The functional characteristics of the most commonly used detectors are described below.
5.5.1 Types and Functions of Vehicular Detectors The type of vehicle detection system used for an actuated signal control depends on the operational requirements of the intersection in terms of the type and use of data needed by the controller to operate efficieVtly. Most. new installations use either inductive loop detectors, magnetic detectors, or magnetometers. The physical design and construction of these commonly used detectors is summarized below: Page 48
TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
(a)
Inductive Loop Detectors : Loop detectors are by far the most commonly used today and are the standard form of detection in many agencies. Essentially, this detector installation consists of a loop which may be one or more turns of wire in a saw-cut slot in the road surface in the exact area where vehicles are to be detected. The ends of this loop are connected by cable to an electronic amplifier usually located in the controller. A vehicle passing over, or resting in the loop, will unbalance a tuned circuit which is sensed by the amplifier.
(b)
Magnetic Detectors : There are three types of magnetic detectors :the standard magnetic detector, a directional magnetic detector, and the magnetometer. All three types consist of two components, an inroad sensor, and an amplifier unit. Although all 3taagnetic detectors operate on the basis of a change in the lines of flux from the earth's magnetic field, the magnetometer is a special type of magnetic detector.
ARAHAN TEKNIK ( JALAN ) 13 / 87
The directional and nondirectional magnetic detector utilizes a coil of wire with a highly permeable core placed beneath the surface of the roadway. When a vehicle comes near or passes over the coil, the constant lines of flux passing through the coil are deflected causing a voltage to by developed in the coil. A high--gain amplifier causes the voltage to operate a relay and transmit to the controller the message that a vehicle has been detected. For these detectors to sense a change in the magnetic field, the vehicle must be in motion. Vehicles travelling less than 10 kmph are generally not detected. Consequently, magnetic detectors can provide the equivalent of passage or motion data, but not occupancy or presence data. (c)
Other Types of Detectors
Earlier detectors that have been use overseas include pressure pads, radar, and sonic detectors. Their use is now very limited. The pressure detector requires a metal frame installed in the pavement to support and hold in place a pressure plate. The detector is activated by the weight of a vehicle causing a closure of contact plates sealed in the rubber pressure plate which Page 49
TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
sends a signal to the controller. This detector is no more in use. Radar detectors operate on the Doppler effect. Microwaves are beamed toward the roadway by a transmitter. A vehicle passing through this beam reflects the microwaves back to the antenna denoting the motion of a vehicle. The sonic detector also uses the Doppler principle. it transmits pulses of ultrasonic energy toward the roadway through a transducer. A vehicle passing through this reflects the energy at a different frequency back to the transducer which denotes a presence or passage of a vehicle. These detectors are of special value, when it is not possible or practical to install loops, magnetic, or magnetometer detectors (e.g., on bridges or approaches with poor base materials). The high-intensity light detector is a special purpose detector system used for priority control for emergency and transit vehicles. It utilizes a high-intensity light emitted at a specific frequency from a transmitter mounted on the vehicle and a detector mounted on or near the traffic signal. When the light from an emergency or priority vehicle is detected, the detector relays a signal to a phase ARAHAN TEKNIK ( JALAN ) 13 / 87
selector connected to the controller. However, this type of detector has never been used in this country.
5.5.2 Application of Vehicle Detectors The application and design of the detection component of actuated traffic signal contol is explicitly related to controller operation which in turn is related to the physical and traffic characteristics of the location. There are a number of ways in which detector application and design can be approached. Detector location and configuration is dependent on a)
Type and capability of controller
b)
Control mode
c)
Traffic variable to be measured
d)
Geometry of the intersection and approaches
e)
Traffic flow characteristics (e.g., volume, speed, etc.)
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TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
Short loop detectors (up to 6 meter in length) constitutes the simplest and most widely used type of detector application. This short loop (small area) configuration is intended to detect a vehicle upstream of the stop' bar. When a vehicle passes over the detector, a "call" is placed and the controller responds as programmed. Short loop detectors may take a number of forms and be located at varying distances upstream of the stop bar depending on the operational requirements. A common application is to space the detector loop about 30m upstream of the stop bar. However this may vary in practise depending on the approaching vehicular speed. Long loop detection can also be used and it is essentially a presence detection in that it registers the presence of a vehicle in the zone of detection as long as the detector is occupied. This method is expensive but multiple small loops could be used to overcome this problem.
5.5.3 Detection of Small Vehicles A presence detector should be able to detect all licensed motor vehicles including a small motorcycle and hold its call until the display of a green to the phase. A hold time of 3 ARAHAN TEKNIK ( JALAN ) 13 / 87
minutes is commonly specified. A conventional detection loop configuration longer than 6 meter may not detect a small motorcycle.
5.6
LOCATION OF DETECTORS Ideally, the detector location should consider the speed, type, and volume of approaching vehicles as well as the type of controller unit. Table 5.1 presents a range of suggested detector setbacks. The values are determined as a function of deceleration rata, reaction time, and deceleration distance. The detector requirements for low-speed approaches differ from the requirements associated with high-speed approaches. Modern controller units are able to detect and register the number of vehicles that. have passed over the detector. With this capability, it is sufficient for a lowspeed approach or an urban condition approach to install just one detector. This detector should be placed about 30m upstream of the stop bar. Adjustments to the variable Initial Green Time can accommodate the traffic built up at the stop bar during the red period. This facility is available in present controller units.
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TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
Table 5. 1 Safe Stopping Distance and Detector Setback ------------------------------------------------------------------------------------------------------Deceleration rate, d = 3.28 m/s Deceleration time, t
=
V/d, seconds
Speed, V
=
m/o
Reaction time, r
=
I second
Reaction Distance, 8
=
r s V metre
Deceleration distance, D
=
l/2 Vt metre
Safe stopping distance, S
= B + D metre = r u V + l/2 Vt -------------------------------------------------------------------------------------------------------
Speed ( km/h )
V ( m/s )
Decel. Time, t ( secs )
Reac. Dist, R ( metre )
Decel. Dist, D ( metre )
Total Dist, S ( metre )
Detector Setback ( metre )
24 32 40 48 56 64 72 80 88 96 105
6.7 8.9 11.2 13.4 15.6 17.9 20.1 22.3 24.6 26.8 29.0
2.20 2.93 3.67 4.40 5.13 5.87 6.60 7.33 8.07 8.80 9.53
6.7 8.9 11.2 13.4 15.6 17.9 20.1 22.3 24.6 26.8 29.0
7.4 13.1 20.5 29.5 40.1 52.5 66.4 81.9 99.2 118.0 138.4
14.1 22.0 31.8 42.9 55.7 70.4 86.5 104.2 123.8 144.8 167.5
14 22 32 43 56 70 * * * * *
* Use multiple detectors
ARAHAN TEKNIK ( JALAN ) 13 / 87
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TRAFFIC SIGNAL CONTROLLERS AND DETECTORS
5.7
INSTALLATION CONSIDERATIONS To operate effectively, detectors must be properly designed and carefully installed. An improperly installed detector can seriously degrade the efficient operation of the controller ' or even render the controller inoperative.
Very large loops of up to 9 meter in width and 16 to 1-8 meter feat in length can provide an extension of green time when occupancy increases to a saturation point in a given direction.
Essentially, the inductive loop detector wire is normally a l3or 14-gauge conductor embedded in a saw-cut slot approximately 75 mm below the pavement. A sealant, such as asphalt, epoxy, polyurethane, or polyester compounds, is used to seal the loop in the pavement. An alternate, more durable construction is to place the turns of wire in a plastic conduit within or just below the pavement surface or within a plastic sleeve laid in the, saw-cut in the pavement. This method is preferred. The width of the loop is normally 1.8 meter while the length can range from 1.8 meter to 30 meter. The effective area of detection normally extends about 0.76 m outside the loop.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 53
CHAPTER 6 TRAFFIC SIGNAL TIMING
6.1
OBJECTIVE The objective of signal timing is to alternately assign the right-of-way to various traffic movements (phases)in such a manner as to minimize average delay to any single group of vehicles or pedestrians and to reduce the probability of accident producing conflicts.
6.2
DESIGN PRINCIPLES
6.2.1 Determination of saturation flow, S The capacity of a traffic-signal controlled intersection is limited by the capacities of the individual approaches to the intersection. This capacity of an approach is measured independently of traffic and other controlling factors and is expressed as the saturation flow. Saturation flow is defined as the maximum flow, expressed as equivalent passenger cars, that can cross the stop line of the approach where there is a continuous green signal indication and a continuous queue of vehicles on the approach. Basic saturation flow (S) expressed in passenger car units per hour with no parked vehicles is given by i)
where effective approach width W > 5.5 m S
ii)
=
525 W p.c.u./hr
and where W < 5,5 m, see Table 6-1.
Where there are parked vehicles, effective approach width is to be reduced by LW where LW
=
14 - 0.9 ( Z-7.6 ) / k
Where Z (>7.6 m) is the clear distance of the nearest parked car from the stop line (m) and k is the green time (sees).
ARAHAN TEKNIK ( JALAN ) 13 / 87
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TRAFFIC SIGNAL TIMING
If the whole expression becomes negative, the effective lose should be taken as zero. The affective loss should be increased by 50 percent for a parked lorry or wide van. Note :
The British formula, assuming m green time of 30 seconds, infers that there is no effect on the approach capacity if parking is approximately 61 m (20O ft) or more away from the stop line.
This basic saturation flow is then has to be corrected for the effect of gradient, turming radium, and the proportion of turning traffic.
Table 6-l Relationship between effective lane width and saturation flow
w(m)
3.0
3.25
3.5
3.75
4.0
4.25
4.5
4.75
5.0
5.25
s ( pcu/h )
1845
1860
1885
1915
1965
2075
2210
2375
2560
2760
a)
Gradient See table below
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Page 55
TRAFFIC SIGNAL TIMING
Table 6-2 Correction factor for the effect of gradient
Correction Factor, Fg
Description
0.85 0.88 0.91 0.94 0.97 1.00 1.03 1.06 1.09 1.12 1.15
b)
for for for for for for for for for for
upward slope of 5% upward slope of 4% upward slope of 3% upward slope of 2% upward slope of 1% for level grade downward slope of 1% downward slope of 2% downward slope of 3% downward slope of 4% downward slope of 5%
Turning radium Saturation flows for approaches with exclusive turning traffic need to be corrected with factor that takes into consideration the magnitude of the turning radius, R. See table below.
Table 6-3 Correction Factor for the effect of turning radius
Correction Factor, Ft 0.85 0.90 0.96
Description for turning radius R < 10 m for turning radius where 10 m < R < 15 m for turning radius where 15 m < R < 30 m
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TRAFFIC SIGNAL TIMING
c)
Turning traffic When u lane comprises straight-on and turning traffic, the proportion of turning traffic is one of the factors determining the saturation flow, S. Table 6-4 specifies correction factors for various percentages of turning traffic over the total traffic on the approach lane.
Table 6-4 Correction factors for turning traffic
% turning traffic
Factor for right-turn, Fr
Factor for left-turn, F1
5 10 15 20 25 30 35 40 45 50 55 60
0.96 0.93 0.90 0.87 0.84 0.82 0.79 0.77 0.75 0.73 0.71 0.69
1.00 1.00 0.99 0.98 0.97 0.95 0.94 0.93 0.92 0.91 0.90 0.89
Note : 1.
If a lane comprises both right and left turning traffic, the total factor will be Fr x Fl
2.
In cases where total saturation flow of the exits is lower than of the approaches, the lower value has to be taken into account.
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TRAFFIC SIGNAL TIMING
6.2.2 Determination of Y value Y = q/S where
y
=
ratio of flow to saturation flow
q
=
actual flow on a traffic-signal approach converted in pcu/hr ( See Table 6-5 for conversion )
S
=
saturation flow for the approach in pcu/hr.
The y value for a phase is the highest y value from the approaches within that phase. n For the whole junction,
Y=
where
E yi
n
=
number of phase
yi
=
highest y value from the approach within that phase i.
This Y value is a measure for the accupancy of the intersection. Y should preferably not be higher than 0.65. If the value found is higher than 0.85, it is recommended that the geometrics of the intersection be upgraded to increase the capacity.
Table 6-5 Conversion factors to pcu's
Vehicle Type
Equipment pcu value
Passenger cars Motor cycles Light vans Medium lorries Heavy lorries Buses
1.00 0.33 1.75 1.75 2.25 2.25
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TRAFFIC SIGNAL TIMING
6.2.3 Determination of total lost time percycle, L From Webster and Cobbe, the total lost time per cycle is n L
where
n
=
E ( I - a ) + E1 I=1 I=1
I
=
the intergreen time between the phases a the amber time, usually taken as 3 seconds.
a
=
the amber time, usually taken as 3 seconds.
1
=
drivers reaction time at begin of green per phase. In practise, this time is set to 2 seconds but 0 - 7 seconds can also be used.
Note : i)
The shortest total lost time is the most economic one because the greater part of the cycle can be used by traffic flows.
ii )
Intergreen, I = R + a (in seconds) where R = all red interval
iii )
To check for adequacy of amber time, a a
=
V ----2A
+
W+L --------V
=
amber time ( sec )
A
=
2 acceleration ( taken as 4.58 m/S )
V
=
approach speed ( m/s )
W
=
width of intersection crossed ( m )
L
=
length of vehicle ( suggested 5.5 m )
where a
ARAHAN TEKNIK ( JALAN ) 13 / 87
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TRAFFIC SIGNAL TIMING
6.2.4 Determination of optimum cycle time, Co An expression for the optimum cycle time, Co,is given in Road Research Technical Paper No. 56 as Co
=
1.5L + 5 ( in seconds ) -----------I-Y
This optimum cycle time, Co, gives the minimum average delay for the intersection. But this delay is not greatly increased if the cycle time varies within the range of 0.75 to 1.50 of the calculated Co. For practical purposes, cycle time should be between 45 seconds to 120 seconds, although an absolute minimum of 25 seconds can be used.
8.2.5 Determination of signal settings Effective green time is the green time plus the change interval minus the lost time for a designated phase. The total effective green time = cycle time minus total lost time. g 1
+
g 2
+ ........... +
g n
=
Co - L
where n denotes the number of phases and gn is the effective green time of phase n. For optimum conditions g 1 -g 2
=
ARAHAN TEKNIK ( JALAN ) 13 / 87
y 1 -y 2
( for a 2 phase cycle )
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TRAFFIC SIGNAL TIMING
With the above ratio, the following formulas apply to each individual phase.
where
g n
=
Yn (Co - L) ---Y
( in seconds )
g n
=
effective green time of the n signal phase
Yn
=
calculated Y-value of the same signal phase.
9 1
=
Yl --Y
( Co L )
g 2
=
Y 2 --Y
(Co L)
For a 2 phase cycle
and
The actual green time, G
=
The controller setting time, K
9+I+R = =
G-a-R g+1-a
Therefore for a two-phase example
and
K 1
=
g+1-a 1
K 2
=
g+I-a 2
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TRAFFIC SIGNAL TIMING
6.2.6 Determination of Capacity a)
Practical capacity, Y prac The maximum possible value of Y which can be accommodated is Y max
=
1-L ----CM
where L
=
total lost time ( sec )
=
maximum cycle time (sec)
C m
* For practical purposes, Cm than Y
=
=
120 seconds
0.9 - 0.0075 L
prac For design purposes Co is used rather than C m. b)
Reserve Capacity, RC This reserve capacity is the difference between the capacity and the actual flow. As a percentage of the present flow, RC is given by RC
=
0.9 ( 1 - L/C max ) - Y x 100% ----------------------------Y
or more conveniently RC
=
Y Y prac -------------------Y
x 100%
Y is the actual value at the junction. A useful mean of calculating RC is by using the Reserve Capacity Diagram in Figure 6-1
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TRAFFIC SIGNAL TIMING
c)
Design Life of Junction, n n
=
where
log ( Q1 /Qo ) -----------------log ( I + GR ) n
=
number of years
Q1
=
90% of ultimate capacity
Q0
=
present flow
MGR =
growth rate
This design life is calculated when C = 120 secs. Therefore all the green times should be adjusted to suit this condition.
6.2.7 Determination of delays and queues a)
Average delay per vehicle on a particular intersection arm is given by
d
where
=
9 --10
2 [C(I-~) ------------[ 2 ( l - ~x )
d
=
average delay per vehicle
c
=
cycle time
~
=
proportion of the cycle that is effectively green for the phase under consideration ( i.e.g/C )
q
=
flow
x
=
degree of saturation, which is the ratio of actual flow to the maximum flow that can pass through the approach ( i.e. q/,.S )
ARAHAN TEKNIK ( JALAN ) 13 / 87
+
2 x ] -----------2q ( l - x ) ]
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TRAFFIC SIGNAL TIMING
To enable the delay to be calculted more easily, the equation is rewritten as. d
where
=
A
and
CA + B/q - K
=
B
=
K
=
2 (1-~) ------------- tabulated in fable 6 - 6 2 ( 1- ~x ) 2 X ------------ tabulated in Table 6 - 7 2(1-x) correction factor tabulated in Table 6 - 8.
Note : User shall use this equation with caution at high degrees of saturation (i.e. x approaches 1) as it will greatly overestimate delay. When x = 1, d = "
b)
Maximum queue occurs at the start of green and has an average value of N
=
qxr
N
=
q ( r/2 + d )
N
=
number of vehicles q = flow ( veh/sec )
d
=
average delay per vehicle for a particular arm ( seconds )
r
=
C - g = effective red time (seconds)
or
where
whichever is greater
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TRAFFIC SIGNAL TIMING
To calculate 'Reserve Capacity' use the left hand diagram to obtain a point corresponding to the 'Lost time' and the maximum cycle time suitable for the junction, extend a line horizontally from this point to the right hand diagram to meet a vertical line corresponding with the Y value - the Reserve Capacity ( RC ) may be read at the point of intersection. Example : Lost Time 10 seconds; Cycle time 75 seconds; Y value 6; Reserve Capacity 30%.
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TRAFFIC SIGNAL TIMING
TABLE 6 - 6 Tabulation of
A
=
(l~2 ) -------------2 ( l - ~x )
----------------------------------------------------------------------------------------------------------------------------x 0.1 0.2 0.3 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.80 0.90 ----------------------------------------------------------------------------------------------------------------------------O.l 0.409 O.337 0.253 0.319 0.188 O.158 0.132 0.107 0.085 0.066 0.048 0.032 0.005 0.2 0.413 0.383 0.261 0.227 0.196 0.166 0.138 0.114 0.091 0.070 0.052 0.024 0.006 0.3 0.418 0.340 0.269 0.236 0.205 0.175 0.147 0.121 0.088 0.076 0.067 0.026 0.007 0.4 0.422 0.348 0.378 0.246 0.314 0.184 0.156 0.130 0.109 0.003 0.063 0.039 0.008 0.5 0.426 0.356 0.288 0.256 0.325 0,195 0.167 0.140 0.114 0.091 0.089 0.033 0.009 0.55 0.423 0.360 0.393 0.362 0.231 0.201 0.172 0.145 0.119 0.095 0.073 0.036 0.010 0.60 0.431 0.364 0.299 0.267 0.237 0,207 0.179 0.151 0.125 0.100 0.078 0.038 0.011 0,65 0.433 0.368 0.304 0.273 0.243 0.214 0.185 0.150 0.131 0.106 0.083 0.042 0.012 0.70 0.435 0.372 0.310 0.280 0.250 0.331 0.192 0.165 0.138 0.113 0.088 0.045 0.014 0.75 0.438 0.376 0.316 0,286 0.257 0.228 0.200 0.172 0.145 0.120 0.095 0.050 0.015 0.80 0.440 0.381 0.322 0.293 0.265 0.236 0.208 0.181 0.154 0.128 0.102 0.056 0.018 0.85 0.443 0.386 0.329 0.301 0.373 0.245 0.217 0.190 8.163 0.137 0.111 0.063 0.021 0.90 0.445 0,390 0.336 0.300 0.281 0.354 0.227 0.200 0.174 0.148 0.123 0.071 0.026 0.92 0.446 0.392 0.388 0.312 8.205 0.258 0.231 0.205 0.179 0.152 0.126 0.076 0.028 0.94 0.447 0.394 0.341 0.315 0.280 0.262 0.236 0.210 0.183 0,157 0.133 0.081 0.032 0.96 0.448 0.396 0.344 0.318 0.292 0,266 0.240 0.215 0.189 0.163 0.137 0.086 0.037 0.98 0.449 0.398 0.347 0.322 0.296 0.271 0.245 0.220 0.194 0.168 0.143 0.083 0.042 -----------------------------------------------------------------------------------------------------------------------------
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TRAFFIC SIGNAL TIMING
TABLE 6 - 7
Tabulation of B
=
2 x ----------2(l-u)
-------------------------------------------------------------------------------------------------x 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 -------------------------------------------------------------------------------------------------0.l 0.006 0.007 0.008 0.0l0 0.0Il 0.013 0.0l5 0.0l7 0.020 0.022 0.2
0.225 0.028 0.031 0.034 0.038 0.042 0.046 0.050 0.054 0.059
0.3
0.064 0.070 0.075 0.081 0.088 0.094 0.101 0.109 0.116 0.125
0.4
0.133 0.I42 0.152 0.162 0.173 0.184 0.l96 0.208 0.222 0.235
0.5
0.350 0.265 0.282 0.299 0.317 0.336 0.356 0.378 0.400 0.425
0.6
0.450 0.477 0.586 0.536 0.569 0.604 0.641 0.680 0.723 0.768
0.7
0.817 0.869 0.926 0.987 1.05
1.13
1.20
1.29
1.38
1.49
0.8
0.60
2.41
2.64
2.91
3.23
3.60
1.73
1.87
2.03
2.21
0.9 4.05 4.60 5.28 6.18 7.36 9.03 11.5 15.7 24.0 49.0 --------------------------------------------------------------------------------------------------
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TRAFFIC SIGNAL TIMING
TABLE 6 - 8 Correction term of equation d as a percentage of the first two terms
=
cA + B - K --q
M x
0.3
0.4
0.5
0.6
0.7
0.8
0.9
~
2.5
5
10
20
40
0.2 0.4 0.6 0.8
2 2 0 0
2 1 0 0
1 1 0 0
1 0 0 0
0 0 0 0
0.2 0.4 0.6 0.8
6 3 2 2
4 2 2 1
3 2 1 1
2 1 1 1
1 1 0 1
0.2 0.4 0.6 0.8
10 6 6 3
4 2 2 1
5 4 3 3
3 2 2 3
2 1 2 2
0.2 0.4 0.6 0.8
14 11 9 7
11 9 8 8
8 7 6 8
5 4 5 7
3 3 3 5
0.2 0.4 0.6 0.8
18 15 13 11
14 13 12 12
11 10 10 13
7 7 8 12
5 5 6 10
0.2 0.4 0.6 0.8
18 16 15 14
17 15 15 15
13 13 14 17
10 10 12 17
7 8 9 15
0.2 0.4 0.6 0.8
13 12 12 14
14 13 13 15
13 13 14 17
11 11 14 17
8 12 12 15
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TRAFFIC SIGNAL TIMING
0.95
0.975
0.2 0.4 0.6 0.8
8 7 7 7
9 9 9 9
9 9 10 10
9 10 11 12
8 9 10 13
0.2 0.4 0.6 0.8
8 8 8 8
9 9 9 10
10 10 11 12
9 10 12 13
8 9 11 14
* M is the average flow per cycle = qc
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TRAFFIC SIGNAL TIMING
6.3
GUIDING PRINCIPLES
period of each approach. (Longer cycle lengths have a higher capacity since over a given time period, there is a lower frequency of starting delays and clearance intervals).
Some guiding principles to be used in accomplishing the objective of this chapter are as follows : a)
b)
The number of phases should be kept to a minimum : each additional phase reduces the effective green time availale for the movement. of traffic flows. (Increases lost time due to starting delays and clearance intervals or intergreen intervals).
-
Short cycle lengths yield the best performance in terms of providing the lowest average delay, provided the capacity of the cycle to pass vehicles is not exceeded. -
For two-phase operations, short cycle lengths (40 to 60 seconds) are generally recommended to produce minimum delay.
-
Longer cycle lengths (over 60 seconds) will accommodate more vehicles per hour if there is a constant demand during the entire green
ARAHAN TEKNIK ( JALAN ) 13 / 87
c)
A 120 second cycle length should be the maximum used, irrespective of the number of phases: above a 120 second cycle, there is an insignificant increase in capacity and rapid increase in total delay.
The level of service of the signalised intersection must be the same as the level of service of the road system at that location. See Tables 6.9 and 6.10 below.
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TRAFFIC SIGNAL TIMING
Table 6 - 9 Level of Service for signalised Intersection
LEVEL OF SERVICE
STOPPED DELAY FOR VEHICLE ( SEC )
A B C D E F
< 5.0 5.1 to 15.0 15.1 to 25.0 25.1 to 40.0 40.1 to 60.0 > 60.0
Table 6.10 Level of service of Road
AREAS
CATEGORY OF ROAD
LEVEL OF SERVICES
RURAL
Expressway Highway Primary Secondary Minor
C C D D E
Expressway Arterial Collector Local Street
C D D E
URBAN
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Page 71
Chapter 7 DESIGN OF PROGRESSIVE SIGNAL TIMING
A signal system is defined as having two or more individual signalised intersections which are link together for coordination purposes. To obtain system coordination all signals must operate with the same (common) cycle length, although in rare instances some intersections within the system may operate at double or one-half the cycle length of the system. Although at. individual intersections, the intervals (red, green, and yellow) may vary according to traffic conditions, it is desirable that the arterial for which coordination is being provided have a green plus yellow interval equivalent to at least 500 of the cycle length.
7.1
iii)
Vehicle speeds should be more uniform because there will be no incentive to travel at excessively high speed to reach a signalized intersection before the start of the green interval, yet slower drivers will be encouraged to speed up to avoid having to stop for a red light.
(iv)
There should be fewer accidents because platoons of vehicles will arrive at. each signal when it is green, thereby reducing the possibility of red-signal violations or rear-end collisions. Naturally, if there are fewer red intervals displayed to the majority of motorists, there is less likely to be Lrouble because of driver inattention, brake failure, slippery pavement, and so on.
v)
Greater obedience to the signal commands should be obtained from both motorists and pedestrian because the motorist will try to keep within the green interval,and the pedestrian
ADVANTAGES Some of the advantages of providing coordination among signals are : (i)
A higher level of traffic service is provided in terms of higher overall speed and reduced number of stops.
(ii)
Traffic should flow more smoothly, often with an improvement in capacity and decrease in energy consumption.
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DESIGN OF PROGRESSIVE SIGNAL TIMING
will stay at the kerb because the vehicles will be closer, spaced. (vi)
7.2
Through traffic will tend to stay on the arterial road instead of on parallel minor roads.
APPLICATIONS In a discussion of the two-way and one-way street applications of system timing, the following terms are frequently used :
7.2.1 One-Way Road The simplest form of coordinating signals is along a oneway road, or to favor one direction of traffic on a twoway road that contains highly directional traffic flows. Essentially, the mathematical relationship between the band speed S and the offset L can be described as S
=
where S = 1.
2.
3.
Through-band : the space between a pair of parallel speed lines which delineates a progressive movement on a time-spare chart. Band speed : the slope of the through-band representing the progression speed of traffic moving along the arterial. Bandwidth : the width of the through-band expressed in seconds (or percent. of cycle length), indicating the period of time available for traffic to flow within the band.
ARAHAN TEKNIK ( JALAN ) 13 / 87
D -------0.278L
(7.1)
speed of progression (km/hr)
D=
spacing of signals (m)
L=
offset in seconds
7.2.2 Two-Way Road For a two-way movement, four general progressive signal systems are possible : (1) simultaneous, (2) alternate, (3) limited (simple) progressive, and (4) flexible progressive. The relative efficiency of any of these systems is dependent on the distances between signalized intersections, the speed of traffic, the cycle length, the road-way capacity, and the amount of friction caused by turning vehicles, parking and unparking maneuvers, improper or illegal parking or loading, and Page 73
DESIGN OF PROGRESSIVE SIGNAL TIMING
pedestrians. In general, a twoway progression with maximum bandwidths can be achieved only if the signal spacings are such that vehicular travel times between signals are a multiple of one-half the common' cycle length : otherwise, inevitable compromises have to be made in the progression design. In a simultaneous system, all signals along a given street operate with the same cycle length and display the green indication at the same time. Under this system, all traffic moves at one time, and a short time later all traffic stops at. the nearest signalized intersection to allow crossroad traffic to move. The mathematical relationship between the band speed (in both directions) and signal spacing in a simultaneous system can be described as follows. S
=
where S =
D -------(7.2) 0.278C speed of progression (km/hr)
D=
spacing of signals (m)
C=
cycle length in seconds
ARAHAN TEKNIK ( JALAN ) 13 / 87
For example, a system of sig nalized intersections at 1/2 km spacing could have a band speed in simultaneous system 30 km/h, respectively, with a 60 sec cycle. With closely spaced intersections, however, a simultaneous system may encourage excessive speeds as drivers tend to travel through a maximum number of intersections during the green interval. In the alternate system, each successive signal or group of signal shows opposite indications to that of the next. signal or group. If each signal alternates with those immediately adjacent, the system is called single alternate. If pairs of signals alternate with adjacent. pairs, the system is termed double alternate: and so on. The band speed in a singlealternate system is S
=
D --------- (7.3) 0.139 C
In a double-alternate system, the band speed is determined by the same formula, with D being the distance between the midpoints of adjacent pairs. Generally speaking, the alternate system may provide excellent traffic; service, depending on the distances between signals and the cycle length. Equal distances provide the best result.
Page 74
DESIGN OF PROGRESSIVE SIGNAL TIMING
In a simle progressive system, a common cycle length is used and the various signal faces controlling a given road provide green indications in accordance with a time schedule to permit continuous operation of platoons along the road at a designed rate of speed, which may vary within different parts of the system. In a flexible progressive system, the signal offsets, splits, and/or cycle length of the common cycle are changed to suit. the needs of traffic : throughout the day. For example, an inbound progression toward the central business district during the morning peak can be changed to an outbound progression during the remainder of the day merely by adjusting the. signal offsets, or a longer cycle length can be used during the morning and evening peak hours in order to provide greater capacity than during the off-peak period.
7.3
PROGRESSIVE SIGNAL SYSTEM DESIGN
equations (7.1) to (7.3) may be solved for C (cycle length) by using the measured operating speed for S and the typical distance between proposed signals for D. The resultant cycle lengths falling in a usable range should be compared with the cycle length computed for each individual intersection. If one cycle length approximates or slightly exceeds those computed for a majority of individual intersection it, should be selected on a trial basis. First, however, each individual intersection must be reexamined to assure that it can operate effectively with the selected cycle length. Sometimes rephasing or geometric and/or operational improvements at an intersection will be required. If such changes are not feasible, and the operation with this cycle length would seriously impaired one. or more intersections, a new trial cycle length should be selected. In practice, the cycle length already established for signal systems intersection or closely adjacent to the system under study will frequently dictate the cycle length to be used.
7.3.1 Selection of a cycle length In the selection of a trial cycle length, the criterion that band speeds be at or near the mean operating speed of vehicles on the street is frequently used. If the spacing in the system is fairly regular, ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 75
DESIGN OF PROGRESSIVE SIGNAL TIMING
7.3.2 Manual design method for arterial routes To develop an arterial-based timing plan, a considerable amount of data must be collected initially, including (i)
Intersection spacing
(ii)
Road geometric
(iii)
Traffic volumes
(iv)
Traffic regulations such as parking, speed limit, and turn restrictions
(v)
Speed and delay information.
Using the data, a number of timing plans are then determined together with the individual timing requirements at each signalized location. For each plan a cycle length is selected which is common to the arterial route, and a graphical analysis of the type illustrated in Figure 7.1. is undertaken by a trial-and-error process to determine offsets for each of the desired timing plans.
intersections. A horizontal working line'is drawn across the graph on which the green or red phase of each signalized intersection at the left edge of the diagram, signal phases are constructed on the vertical reference line with either a green or red phase centered on the working line. A progression speed line which has a slope representing the desired progression speed is drawn starting at the beginning of the green phase at the first signalized intersection. Far each succeeding intersection, either a red or green signal phase is centered on the horizontal working line to obtain an equal bandwidth for each direction of flow. Should progressive movement, be desired in only one direction, this procedure may be modified such that the beginning of the green phase at each intersection is placed on the progression speed line.
Figure 7.1 is a two-dimensional graph portraying a twodirectional coordinated arterial system with distance on the horizontal scale and time on the vertical scale. The intersections are located on the distance scale with vertical reference lines drawn at the centerline of all signalized ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 76
DESIGN OF PROGRESSIVE SIGNAL TIMING
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 77
BIBLIOGRAPHY
1.
"Highway Capacity Manual 1965" - Highway Research Board Special Report 87, Washington DC, 1965.
2.
Homburger, Wolfgang S, & Kell, James H, "Fundamentals of Traffic Engineering - 10th Ed., "Institute of Transportation Studies, Univ. of California, Berkely, California 1981.
3.
Kell, James H & Fullerton, Iris J. "Manual of Traffic Signal Design", Institute of Transportation Engineers, New Jersey 1982.
4.
Pignataro, Louis J, "Traffic Engineering, Theory and Practise," Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1973.
5.
"Practical Guide for Planning and Design of At-Grade Intersection" Japan Society of Traffic Engineers, April 1985.
6.
"Traffic: Engineering Handbook", Institute of Traffic Engineers, Washington 1965.
7.
Webster, F.V. and Cobbe, B.M. "Traffic Signals" - Ministry of Transport, Road Research Technical Paper No. 56, London, April 1966.
8.
Yu, Jason C, "Transportation Engineering, Introduction to Planning, Design, and Operations", Elsevier, New York 1982.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 78
BIBLIOGRAPHY
Intergreen period : The period of time between the termination of the green signal for one phase and the beginning of the green signal for the next phase to receive right of way. Interval :
A discrete portion of the signal cycle during which the signal indications remain unchanged. Interval Sequence: Specifies the order in which the various intervals are displayed.
Interval Timing :
The passage of time which occurs during an interval.
Loop Detector :
A device capable of sensing a change in inductance of a loop sensor imbedded in the roadway caused by the passage or presence of a vehicle over the loop.
Maximum extension :
Difference between maximum green and minimum green. The normal cycle time + max extension times should preferably not, exceed 120 sees.
Maximum green :
The maximum (preset) period a green signal can last after a demand has been made by traffic on another phase.
Magnetometer :
A device capable of being actuated by the magnetic disturbance caused by the passage or presence of a vehicle. A magnetic flux generator/sensor is installed in the roadway and connected to sensor applifier electronics.
Measures of Effectiveness(MOEs) :
Indices of the effectiveness of the system in improving traffic flow. Common bases of comparison include congestion, density, lane occupancy, stops, delay, and queue length.
Minimum green :
The shortest period of time a green signal may be displayed during any phase.
Occupancy :
The percentage of roadway occupied by vehicles at an instant in time. In general use, it is a measurement based upon the ratio of vehicle presence time (as indicated by a presence detector) over a fixed per:rod of total time.
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BIBLIOGRAPHY
Offset :
The time difference or interval in seconds between the start of the green indication at one intersection as related to the start of the green interval at another intersection or from a system time base.
Offset Selection :
Choosing one of several possible offsets either manually or automatically either by time-of-day or in response to some directional characteristics of traffic flow.
Parameter : (1) A quantity in mathematics that, may be assigned any arbi trary value and that remains constant during some calculation; (2) a definable characteristics of an item, device, or system. Pattern :
A unique set. of traffic parameters (cycle, split., and offset) associated with each signalized intersection within a predefined group of intersection (a section or subzone)
Phase :
A part of the traffic signal time cycle: allocated to any combination of traffic movements receiving right of way simultaneously during one or more intervals.
Phase Overlap :
Refers to a phase which operates concurrently with one or more other phases.
. Phase Sequence :
Plan :
The order in which a controller cycles through all phases.
A plan gives the relationship between phases and signal groups in terms of time. The possibilities of a plan can be laid down in a time cycle diagram of one or more intersection control units.
Presence Detection :
The sensing of a vehicle passing over a detector. True presence is when the pulse duration is equal to the actual time the vehicle remains in the detector field of influence.
Primary Signal Face :
The signal face which is nearest to and facing oncoming traffic. It is ordinarily situated on the near side of the carriageway facing approaching traffic, but may be duplicated on the off-side.
Recall :
An operational mode for an actuated intersection controller whereby a phase, either vehicle or pedestrian is displayed each cycle whether demand exists or not. Usually a temporary emergency situation.
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Page 80
BIBLIOGRAPHY
Relay :
An electromagnetic switching device, having multiple electrical contacts, energized by electrical current through its coil. It is used to completed electrical circuits.
Saturation flow :
The maximum flow that can pass through an intersection approach under prevailing traffic and roadway conditions, assuming that the approach had 100% of real time available as effective green time.
Secondary Signal Face :
A signal face facing on-coming traffic supplementing the primary signal face and remote from it.
Signal group :
A set of one or more signal indications which are switched on and off simultaneously.
Signal Head :
An assembly containing one or more signal faces that may be designated accordingly as one-way, two-way, etc.
Signal Indication :
The following of a traffic signal lens or equivalent device or a combination of several lenses or equivalent: devices at the same time.
Signal face : That. part, of a signal head that contains lenses and associated components (such as bulbs, reflectors, visors) provided for con trolling traffic in a single direction. Turning indications may be included in a signal face. Split : A percentage of the cycle length allocated to each of the various phases in a signal sequence. Stops :
The number of times vehicles stop in the system. Used as a measure of effectiveness to assess the effectiveness of a timing pattern. A computer controlled system goal is to minimize stops.
traffic :
Vehicles, persons or animals, traveling on a highway considered collectively.
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Page 81
APPENDIX A Design Example This example consists of step by step design calculations to further explain the concepts found in Chapter 6. The junction's geometric and traffic flow values for this design example are only hypothetical
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Page 82
APPENDIX A
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Page 83
APPENDIX A
2.
Peak-hour flows The peak-hour flows are obtained from 16-hour classified traffic counts and data are converted into pcu's by using the factors in Table 6-5. The converted values are as shown :-
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 84
APPENDIX A
An average value of the morning and evening peak is than tabulated.
FROM APPROACH
DIRECTION
NORTH Total pcu : 218
LT : 48 ST : 135 RT : 35
SOUTH Total pcu : 281
LT : 53 ST : 180 RT : 48
EAST Total pcu : 439
LT : 78 ST : 193 RT : 168
WEST Total pcu : 423
LT : 98 ST : 145 RT : 180
Projected design values
Lets say the project will be implemented the following year. So, n = 1 and with GR = 5% (assume).
PCU = future
1 PCU x (1.05) present
With this formula the following design values are use for signal design calculations.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 85
APPENDIX A
Design value
Approach from
Total pcu
Movement pcu
NORTH
229
LT : 50 ST : 142 RT : 37
SOUTH
295
LT : 56 ST : 189 RT : 50
EAST
461
LT : 82 ST : 203 RT : 176
WEST
444
LT : 103 ST : 152 RT : 189
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 86
APPENDIX A
3.
Saturation flows The information for the approaches permits the following calculations : NORTH :
S = 1965 pcu/hr for W = 4.Om ( from table 6-1 ) Factors Gradient : Fg = 1.09 for -3% grade ( table 6-2 ) Left-turn Traffic : ( 50/229)x100%=22%, F1=0.98 ( table 6-4 ) Right-turn Traffic : (37/229)x100%=16%, Fr= 0.90 ( table-6-4 ) Adjusted saturation flow S
SOUTH :
= = =
S x Fg x F1 x Fr 1965 x 1.09 x 0.98 x 0.90 1889 pcu/hr
S = 1965 pcu/hr for W = 4.Om (from table 6-1) Factors Gradient : Fg = 0.91 for +3% grade ( table 6-2 ) Left-turn Traffic : ( 56/295)x100%=19%, F1=0.98 ( table 6-4 ) Right-turn Traffic : ( 50/295)x100%=17%, Fr=0.89 ( table 6-4 ) Adjusted saturation flow Ss
= = =
ARAHAN TEKNIK ( JALAN ) 13 / 87
S x Fg x Fl x Fr 1965 x 0.91 x 0.98 x 0.89 1560 pcu/hr
Page 87
APPENDIX A
EAST : a)
Left Lane : S = 1915 pcu/hr for W = 3.75 m ( from table 6-1 )
Factors Gradient : Fg = 1.0 for level grade ( table 6-2 ) Left-turn Traffic : (82/285)x100%=29%, F1=0.95 ( table 6-4 ) Adjusted saturation flow S EL
b)
=
S x Fg x Fl
= =
1915 x 1.0 x 0.95 1819 pcu/hr
Right Lane : S = 1915 pcu/hr for W = 3.75 m ( from table 6-1 )
Factors Gradient : Fg = 1.0 for level grade ( table 6-2 ) Turning Radius : Ft = 0.85 for R < 10m ( table 6-3 ) Adjusted saturation flow S
= = =
S x Fg x Ft ER 1915 x 1.0 x 0.85 1628 pcu/hr
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 88
APPENDIX A
WEST : a)
Left Lane : S = 1915 pcu/hr for W = 3.75 m ( from table 6-1 )
Factors Gradient : Fg = 1.0 for level grade ( table 6-2 ) Left-turn Traffic : ( 103/255)x100%=40%, F1=0.93 ( table 6-4 ) Adjusted saturation flow S EL
b)
=
S x Fg x F1
= =
1915 x 1.0 x 0.93 1781 pcu/hr
Right Lane : S = 1915 pcu/hr for W = 3.75 m ( from table 6-1 )
Factors Gradient : Fg = 1.0 for level grade ( table 6-2 ) Turning Radius : Ft = 0.85 for R < 10 m ( table 6-3 ) Adjusted saturation flow S ER
=
S x Fg x Ft
= =
1315 x 1.0 x 0.85 1628 pcu/hr
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 89
APPENDIX A
The next step is to determine the phasing for the intersection. For the purpose of this example, let's consider a 3 phase fixed time traffic signal with the phases including pedestrian phase are as shown below.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 90
APPENDIX A
Y - VALUE
PHASE
¢1
MOVE MENT WL IDENTIFICATION
¢2
¢1
EL
WR
ER
M
S
285
189
179
229
295
q
225
s
1781 1817
1628 1628
1889 1560
q/s
0.143 0.157
0.116 0.108
0.121 0.189
Y
0.157
EY
= =
0.116
0.189
0.157 + 0.116 + 0.189 0.462
SINCE EY < 0.85 ( Which is the limiting value ) WE CAN PROCEED WITH THE TIMING CALCULATIONS.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 91
APPENDIX A
5.
Amber time, a The amber time (a) for the North and South approaches are the same since vehicles from that approach has to travel 12.25m to clear the intersection. a
= N and S
= =
a
6.
= E and W
13.4 m/s 12.25 m + 5.5 m ----------------- + ---------------------2 x 4.58 m/s 13.4 m/s 2.79 3 seconds
13.4 m/s 9 m + 5.5 m ----------------- + ------------------2 x 4.58 m/s 13.4 m/s
= =
2.54 3 seconds
Use a =
3 seconds
Intergreen time, I I=a+R where R = all red interval ( taken as 2 seconds ) Therefore, I = =
7.
3+2 5 seconds
Total lost time, L n L
=
n E(I-a)+ E1 i=1 i=1
= =
3 ( 5-3 ) + 3 ( 2 ) 12 seconds
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 92
APPENDIX A
8.
Optimum cycle time, Co Co
=
1.5L + 5 ----------1-Y
=
1.5 ( 12 ) + 5 -----------------1 - 0.462
=
43 seconds
Design Co can be between 0.75 to 1.50 of the calculated Co. For simplicity, take design Co = 60 seconds
9.
Total effective green time Total effective green time = = =
10.
Co - L 60 - 12 48 seconds
Effective green time, g g
=
y(C-L) -Y
g 01
=
0.157 ( 48 ) --------------0.462 16 seconds
= g 02
=
= g 03
=
=
0.116 ( 48 ) --------------0.462 12 seconds 0.189 ( 48 ) --------------0.462 20 seconds
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 93
APPENDIX A
11.
Actual Green Time, G Gi
=
gi+li+Ri
( in this worked example, all the 1's and R's are the same for every phase ).
12.
G 01 = =
16 + 2 + 2 20 seconds
G 02 = =
12 + 2 + 2 16 seconds
G 03 = =
20 + 2 + 2 24 seconds
Check for pedestrian requirement for green time G = ped
5+
W ------ - I 1.22
( Note: Check only the critical pedestrian crossings where W is the widest ) G
=
5+
9 -----1.22
= =
7.38 8 seconds
-5
In our calculations, green time available for pedestrian crossing is in phase 1. G
=
20 seconds, therefore it is O.K.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 94
APPENDIX A
13.
Controller setting time, K Ki
15.
=
Gi-a-R
K 01 = =
20 - 3 - 2 15 seconds
K 02 = =
16 - 3 - 2 11 seconds
K 03 = =
24 - 3 - 2 19 seconds
Reserve Capacity of Junction R.C.
=
Let Cm
=
0.9 ( 1-L ) - Y --Cm ------------------- x 100% Y 120 seconds
From the above calculations :
R.C. =
=
L = 12 seconds, Y = 0.462
0.9 ( 1-12/120 ) - 0.462 -------------------------------- x 100% 0.462 75%
The Reserve Capacity Diagram, by using Figure A - 2, RC = 75%.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 95
APPENDIX A
16.
Design Life of the junction, n
n
=
log ( Q1/Qo ) ----------------log ( 1 + GR )
Assume GR = 5%
Q is the practical capacity that can be accomodated with 120 seconds cycle. For ease, the variables for each approach are tabulated as below.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 96
APPENDIX A
Movement
N
S
W
W
L
S g Co Capacity Q = gS / C 90% ult. cap Ql Present flow Qo
Note :
E
R
E L
R
1889 44 120
1560 44 120
1781 37 120
1628 27 120
1819 37 120
1628 27 120
693
572
549
366
561
366
624
515
494
329
505
329
229
295
255
189
285
176
The above g values are calculated when Co = 120 sec
Then check for various movements. N:
S:
WL :
Ql Go GR
Ql Qo GR
01 Qo GR
= = =
= = =
= = =
624 229 5%
515 295 5%
494 255 5%
ARAHAN TEKNIK ( JALAN ) 13 / 87
n
n
n
=
log ( 624/229 ) -------------------log ( 1 + 0.05 )
=
21 years
=
log ( 515/295 ) ------------------log ( 1 + 0.05 )
=
11 years
=
log ( 494/255 ) ------------------log ( 1 + 0.05 )
=
14 years
Page 97
APPENDIX A
WR : Q1 Go GR
EL :
ER :
Q1 Go GR
Q1 Qo GR
= = =
= = =
= = =
329 189 5%
505 285 5%
329 176 5%
n
n
n
=
log ( 329/189 ) ------------------log ( 1 + 0.05 )
=
11 years
=
log ( 505/285 ) ------------------log ( 1 + 0.05 )
=
12 years
=
log ( 329/176 ) ------------------log ( 1 + 0.05 )
=
13 years
Design Life, n = 11 years
17.
Delays N
:
q= S= g= C=
229 pcu/hr = 229/3600 pcu/sec 1889 pcu/hr 20 60
~=
g/C = 20/60 = 0.333
x=
q= ~S
=
229 ----------------0.33 ( 1889 )
0.36
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 98
APPENDIX A
dN
S:
dS
=
9 --10
=
[ 60 ( 1-0.333 )² 0.362² ] ------------------------- + -------------------------[ 2( 1-0.333x0.36 ) 2 ( 229 )( 1-0.36 ) ] -------3600 0.9 ( 15.16 + 1.59 )
=
15 seconds
q S g C
= = = =
295 pcu/hr = 295/3600 pcu/sec 1560 pcu/hr 20 60
~
=
9/C = 20/60 = 0.333
x
=
q --~S
=
0.57
=
9 --10
[ 60 ( 1-0.333 )² 0.572² ] ------------------------ + --------------------------[ 2( 1-0.333x0.57 ) 2( 295 ) ( 1-0.577 ) ] -------3600
=
0.9 ( 16.47 + 4.61 )
=
19 seconds
=
295 ----------------0.33 ( 1560 )
WL : q S g C
= = = =
255 pcu/hr = 255/3600 pcu/sec 1781 pcu/hr 16 60
~
=
g/C = 16/60 = 0.27
x
=
q --~S
=
0.53
ARAHAN TEKNIK ( JALAN ) 13 / 87
=
255 ----------------0.27 ( 1781 )
Page 99
APPENDIX A
d WL
=
9 --10
[ 60 ( 1-0.27 )² 0.532² ] ---------------------- + --------------------------[ 2 ( 1-0.27x0.53 ) 2( 255 ) ( 1-0.53 ) ] -------3600
=
0.9 ( 18.66 + 4.22 )
=
21 seconds
WR = q S g C
= = = =
189 pcu/hr = 189/3600 pcu/sec 1628 pcu/hr 12 60
~
=
g/C = 12/60 = 0.2
x
=
q --~S
=
0.58
=
9 --10
[ 60 (1-0.2 )² 0.582² ] --------------------- + ---------------------------[ 2( 1-0.2x0.58 ) 2( 189 ) ( 1-0.58 ) ] ------3600
=
0.9 ( 21.72 + 7.63 )
=
26 seconds
q S g C
= = = =
285 pcu/hr = 285/3600 pcu/sec 1819 pcu/hr 16 60
~
=
g/C = 16/60 = 0.27
d WR
EL :
ARAHAN TEKNIK ( JALAN ) 13 / 87
=
189 --------------0.2 ( 1628 )
Page 100
APPENDIX A
x
dEL
ER :
dER
=
q --~S
=
=
0.58
=
9 --10
[ 60(1-0.27)² 0.58² ] ---------------------- + -----------------------[ 2( 1-0.27x0.58 ) 2( 285) (1-0.58) ] ------3600
=
0.9 ( 18.96 + 5.06 )
=
22 seconds
q S g C
= = = =
176 pcu/hr = 176/3600 pcu/sec 1628 pcu/hr 12 60
~
=
g/C = 12/60 = 0.2
x
=
q --~S
=
0.54
=
9 --10
[ 60 ( 1-0.2 )² 0.542² ] ---------------------- + -------------------------[ 2 ( 1-0.2x0.54 ) 2( 176 ) ( 1-0.54 ) ] ------3600
=
0.9 ( 21.52 + 6.48 )
=
25 seconds
=
285 ------------------0.27 ( 1819 )
176 ---------------0.2 ( 1628 )
Therefore movement WR will experience the worst delay of 26 seconds per vehicle. Its condition will be in the level of service D. Other approaches will be in level of service C.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 101
APPENDIX A
18.
Queue lengths, N NORTH :
q g C d r
= = = = =
229 pcu/hr 20 s 60 s 15 s 40 s
a)
N
= 229 x 40 -----------3600
=
2.54 pcu
Assume 1 vehicle = 1.2 pcu. This value depends on the composition of the present traffic flow i.e. if more medium and heavy vehicles than cars, the value should be more than 1.
b)
N
N
= =
2.54/1.2 2.12 vehicles
=
229 ( 40/2 + 15 ) ----------------------3600
= = =
2.23 pcu 2.23/1.2 vehicles 1.86 vehicles
Therefore, the North approach will experience an average queue length of 2.1 vehicles.
SOUTH :
q g C d r
= = = = =
295 pcu/hr 20 s 60 s 19 s 40 s
a)
N
=
295 x 40 -----------3600
= =
3.28/1.2 2.73 vehicles
ARAHAN TEKNIK ( JALAN ) 13 / 87
=
3.28 pcu
Page 102
APPENDIX A
b)
N
=
295 ( 40/2 + 19 ) ---------------------3600
= = =
3.20 pcu 3.20/1.2 vehicles 2.67 vehicles
Therefore, the South approach will experience an average queue length of 2.73 vehicles.
WEST :
a)
b)
q g C d r
= = = = =
255 pcu/hr 16 s 60 s 21 s 44 s
N
=
255 x 44 -----------3600
= =
3.12/1.2 2.6 vehicles
=
255 ( 44/2 + 21 ) ----------------------3600
= = =
3.05 pcu 3.05/1.2 vehicles 2.54 vehicles
N
=
3.12 pcu
Therefore, the West left lane approach will experience an average queue length of 2.6 vehicles.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 103
APPENDIX A
WESTR :
q g C d r
= = = = =
189 pcu/hr 12 s 60 s 26 s 48 s
a)
N
=
189 x 48 -----------3600
N
= =
2.52/1.2 2.1 vehicles
N
=
189 ( 48/2 + 26 ) ---------------------3600
= = =
2.63 pcu 2.63/1.2 vehicles 2.19 vehicles
b)
=
2.52 pcu
Therefore, the West right lane approach will experience an average queue length of 2.19 vehicles.
EASTL :
q g C d r
= = = = =
285 pcu/hr 16 s 60 s 22 s 44 s
a)
N
=
85 x 44 ---------3600
= =
3.48/1.2 2.9 vehicles
=
285 ( 44/2 + 22 ) ---------------------3600
= = =
3.48 pcu 3.48/1.2 vehicles 2.9 vehicles
b)
N
ARAHAN TEKNIK ( JALAN ) 13 / 87
=
3.48 pcu
Page 104
APPENDIX A
Therefore, the East left lane approach will experience an average queue length of 2.9 vehicles.
EASTR :
q g C d r
= = = = =
176 pcu/hr 12 s 60 s 25 s 48 s
a)
N
=
176 x 48 -----------3600
= =
2.35/1.2 1.96 vehicles
=
176 ( 48/2 + 25 ) ---------------------3600
= = =
2.4 pcu 2.4/1.2 vehicles 2 vehicles
b)
N
=
2.35 pcu
Therefore, the East right lane approach will experience an average queue length of 2 vehicles.
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 105
APPENDIX B Vehicle - actuated Signal Facilities
ARAHAN TEKNIK ( JALAN ) 13 / 87
Page 106
APPENDIX B
Vehicle-actuated signals have largely replaced fixed-time signals because of their greater flexibility under varying traffic conditions. With vehicle-actuated signals several facilities are available to increase the response of the signals to traffic demand; one of these is the minimum green period. The minimum green period is the shortest. period of right of way that. is given to any phase. It is long enough to clear the vehicles waiting between the detector loop and the stop line. Modern controllers have minimum green periods that vary between 7 and 13s, according to the number of vehicles that have passed the detector and are waiting at, the stop line. The minimum green period may be extended beyond the minimum value as vehicles pass over the detector on the approach. With a modern signal controller the length of this vehicle extension period is related to the measured speed of approach at the detector. These vehicle extension periods are individually and not. cumulatively set so that the green period is not reset if a new vehicle extension period calculated by the controller does not exceed the unexpired portion of the previous controller.
The application of successivevehicle extension periods would result in a continuous green indication if there was a continuous passage of vehicles along the approach. To limit the length of the green period there is preset maximum green period, which is normally set at, a value between 8 and 68s, although on holiday routes some controllers allow this period to be increased by a further two minutes. When signals run to maximum green then, on the expi.ry of the maximum green period on the other phase or phases, provision is made for the return of the right. of way to the original phase. In practice when traffic is heavy on all approaches, the signals run to maximum green on all phases and in effect give fixed-time operation. A variation of this maximum green period is the variable maximum period. This facility allows the maximum green to be extended if the flow at the end of the maximum green period exceeds a certain critical value. This critical value is constantly increased until it exceeds the measured flow or a gap change occurs. Note :
If an interval of time between vehicles crossing the detector becomes greater than the last. vehicle extension period, and if there has been a demand for the green signal on another phase, then a 'gap change' takes place and the right of way is transferred. ARAHAN TEKNIK ( JALAN ) 13 / 87
This article is taken from 'Highway Traffic Analysis and Design' Rev. Ed. London: The Mac Millan Press Ltd, 1976 by R.J. Salter.
Page 107
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