RTA Road Design Guide

ROADS AND TRAFFIC AUTHORITY OF NSW

ROAD DESIGN GUIDE TABLE OF CONTENTS GLOSSARY OF TERMS

December 1989

SECTION 1: BASIC DESIGN CRITERIA

August 1991

Amended

August 1996

SECTION 2: ROAD GEOMETRY

March 1988

SECTION 3: CROSS SECTION

Issue 1.0 June 1999 Revision 1.1 Feb 2000

SECTION 4: INTERSECTIONS AT GRADE

Issue 1.0 May 1999 Revision 1.1 Jan 2000

SECTION 5: DRAFT DESIGN OF EARTH STRUCTURES

February 1989

WITHDRAWN - September 2003 - (If information required on this SECTION – Contact sender)

SECTION 6: SAFETY BARRIERS FOR ROADS AND BRIDGES

May 1996

SECTION 7: DRAFT DRAINAGE

September 1991

SECTION 8: EROSION AND SEDIMENTATION

April 1993

SECTION 9: MISCELLANEOUS 9.1 Auxiliary Lanes

August 1988

SECTION 2 ROAD GEOMETRY

CONTENTS 2.1 2.2 2.3 2.4

SIGHT DISTANCE HORIZONTAL ALIGNMENT VERTICAL ALIGNMENT CO-ORDINATION OF HORIZONTAL AND VERTICAL ALIGNMENT

Roads and Traffic Authority Road Design Guide March 1988

2.1

SIGHT DISTANCE

2.1.1

General

2.1.2

Sight Distances

2.1.3

Constants assumed for determination of sight distances

2.1.4

Stopping sight distance

2.1.5

Effect of grade on braking distance

2.1.6

Overtaking sight distance

2.1.7

Intermediate sight distance

2.1.8

Summary of sight distances

2.1.9

Sight distance at night

2.1.10

Sight distance at vertical sags

2.1.11

Sight distance at vertical crests

2.1.12

Sight distance at horizontal curves

2.1.13

Benching for visibility on horizontal curves

2.1.14

Sight distance at combined horizontal and vertical curves

2.1.15

Sight distance at intersections

2.1.16

Sight distance on undivided roads

2.1.17

Sight distance on divided roads

2.1.18

Sight distance through underpasses

2.1.19

Sight distance at interchanges

2.1.20

Other restrictions to visibility

2.1.21

Effect of no-overtaking zone markings

Page No.

2.2

HORIZONTAL ALIGNMENT

2.2.1

General

2.2.2

Straight alignment

2.2.3

Curved alignment

2.2.4

Horizontal curve radius

2.2.5

Length of curved roadway

2.2.6

Circular arc

2.2.7

Deflection angle

2.2.8

Vehicular movement on a circular path

2.2.9

Transverse friction

2.2.10

Superelevation - general

2.2.11

Desirable superelevation

2.2.12

Maximum values of superelevation

2.2.13

Minimum values of superelevation

2.2.14

Adverse crossfall

2.2.15

Superelevation on bridges

2.2.16

Superelevation on steep grades

2.2.17

Superelevation at road junctions

2.2.18

Superelevation development a. b. c. d. e.

2.2.19

Length of superelevation development Procedure Rate of Rotation Relative grade Length of superelevation development to satisfy relative grade

Plan transition a. Clothoid spiral b. Cubic parabola

2.2.20

Lane widening

2.2.21

Compound curves a. Radii b. Length

2.2.22

Broken back curves

2.2.23

Reverse curves

2.2.24

Sight distance on horizontal curves

Page No.

2.3

VERTICAL ALIGNMENT

2.3.1

General

2.3.2

Grading

2.3.3

Grading at intersections

2.3.4

Vertical curves

2.3.5

Length of vertical curves for appearance

2.3.6

Length of vertical curves for comfort

2.3.7

Length of vertical curves for sight distance requirements

2.3.8

Sight line constant for crest curves

2.3.9

Length of crest curves

2.3.10

Sag vertical curves

2.3.11

Sight line constant for sag curves

2.3.12

Determination of lengths for sag curves

2.3.13

Overhead obstruction at sag curves

2.3.14

Vertical curves on undivided roads

2.3.15

Vertical curves on divided roads

2.3.16

Calculation of parabolic vertical curves

Page No.

2.4

CO-ORDINATION OF HORIZONTAL AND VERTICAL ALIGNMENT (This subject is more fully covered in Section 6)

2.4.2

General

Page No.

SECTION 2

NOTATION

A

Algebraic difference of vertical grades (%).

a

Vertical component of acceleration (m / sec2).

B

Benching offset (m).

C

Sight line constant for vertical curves.

Ca

Length of circular arc (m).

Cl

Lateral clearance between vehicles in adjacent lanes (m).

CL

Base control line.

Dh

Headlight illumination distance (m).

Dm

Intermediate sight distance (m).

Do

Overtaking sight distance (m).

Ds

Stopping sight distance (m).

d

Braking distance (m).

dr

Distance travelled during reaction time (m).

E

Superelevation (%).

e

Superelevation (m / m or tangent of angle).

f

Assumed value of transverse friction demand.

fl

Assumed coefficient of longitudinal friction demand.

G

Longitudinal grade (%).

Gr

Relative grade (%).

g

Acceleration due to gravity (9.8m / sec2).

H

Clearance of overhead obstructions (m).

h

Mounting height of headlight (m).

h1

Height of eye above road (m).

h2

Object cutoff height above road (m).

K

Measure of vertical curvature.

L

Length of vertical curve (m).

Le

Length of superelevation development (m).

Lh

Length of horizontal curve (m).

Lp

Length of plan transition (m).

SECTION 2 NOTATION (continue) Lr

Length of crossfall rotation (m).

Lx

Length of a vehicle between its rear axle and the limit of its front overhang (m).

n

Normal crossfall (%)

P

Spiral transition factor

p

Spiral transition offset (m).

Q

Rate of change of grade per unit length (% / m).

R

Horizontal curve radius (m).

Rt

Reaction time (secs).

S

Maximum plan transition offset for cubic parabola (m).

S.C. Spiral curve, common point of spiral and circular curve. S.S. Start of superelevation transition. T.P. Tangent point, common point of tangent and circular curve. T.S. Tangent spiral, common point of tangent and spiral. V

Speed (km / h).

v

Speed (m / sec).

Vm

Distance between adjacent T.S. points on broken-back or reverse curves (m).

W

Lane widening (m).

Wa

Distance rear wheels track inside front wheels on curve (m).

Wb

Extra width allowance for difficulty of driving on curve (m).

Wd

Additional width of front overhang on curve (m).

We

Distance from inside lane line to driver position (m).

Wl

General lane width (m).

Wn

Width of pavement on tangent (m).

Wr

Width from axis of rotation to outside edge of running lanes (m).

Ws

Width of inner travel lane and adjacent shoulder (m).

x

Distance of offset from either the T.S. or S.C. end of plan transition (m).

y

Intermediate offsets of plan transition (m).

θ

Elevation angle of headlight beam (+ø upwards).

∠°

Deflection angle (degrees).

RTA of NSW

Section 2 - Road Geometry

2.1 SIGHT DISTANCE

Reaction Time

2.1.1 General A principal aim in road design is to ensure that a driver has sufficient sight distance to be able to perceive any road hazards in sufficient time to take action to avoid mishap. A driver's sight distance should be as long as practicable, but it is often restricted by crest vertical curves, horizontal curves in cutting, roadside vegetation and buildings at intersections. These restrictions can make manoeuvres such as overtaking unsafe due to the sight restriction. The provision of adequate sight distance therefore requires a determination of the length of crest vertical curves and radius of horizontal curves to suit the desired sight distance. Where the desired radius of horizontal curve cannot be achieved, it becomes necessary to determine the extent to which the inside of the curve should be cleared to allow the driver to see the required distance along the road.

Driver Eye Height

Object Height

Stopping sight distance is the minimum distance required by an average driver of a vehicle travelling at a given speed to react and stop before reaching an object in the vehicle path. Stopping sight distance is measured along the line of travel from a point 1.15m high (representing the height of a driver's eye), to a point 0.2m high (representing a stationary object on the roadway). The length of vertical curve required at crests increases significantly as the object cut off value approaches zero and therefore the general figure adopted which produces satisfactory designs is 200mm. However, zero should be used in the case of intersections where it is necessary to see road markings, or on the approaches to causeways and floodways where water or sand left by floods, or washouts may occur (see Figure 2.3.3). Stopping sight distance has two components, the distance travelled during total reaction time and the distance travelled during braking time.

In design there are three sight distance requirements to be met : (i) Stopping Sight Distance At all times a driver must be provided with sufficient visibility to see an object in the lane of travel and stop before striking it. This is known as the "stopping" sight distance. (ii) Overtaking Sight Distance At reasonable intervals a driver should have sufficient visibility to detect oncoming vehicles in sufficient time to allow safe and uninterrupted overtaking of a vehicle with minimal risk of collision with oncoming traffic. This is known as the "overtaking" sight distance. (iii) Intermediate Sight Distance Although the provision of overtaking sight distance is desirable, the cost of construction to achieve it can be prohibitive. The provision of "intermediate" sight distance enables a driver to travel a road in comfort with reasonably safe overtaking opportunities. Calculations to obtain the distance needed to stop or to overtake are made on the assumption that the driver is travelling at a speed consistent with the alignment of the road. In practice, the actual speed adopted by a driver is influenced by geometric features of the road layout rather than the sight distance provided.

Reaction distance (dr)

= Rt v =

Rt V 3.6

v2 V2 Braking distance (d) = = 2 gf l 254 f l Stopping Sight Distance (Ds)

RtV V2 = + 3.6 254 f l Where: dr= distance travelled during reaction time d= distance travelled during braking time Ds= stopping sight distance (m) Rt= reaction time (secs) v = speed (m/s) V = speed (km/h) fl = assumed coefficient of longitudinal friction demand (regarded as constant throughout the braking period (see Table 2.1.1). g= acceleration due to gravity (9.8m/sec2)

Constants Assumed for Determination .of Sight Distances

The stopping sight distance to be used for various speeds on level bituminous or concrete surfaces are shown in Table 2.1.1.

The following values are used in calculating stopping distances and sight distances (see Figure 2.1.1). Road Design Guide

-- 1.15m Approaching Vehicle. -- 0.2m Stationary object on road. -- 0.6m Vehicle tailstop light.

2.1.4 Stopping Sight Distance

2.1.2 Sight Distances

2.1.3

-- 1.5 secs for design speeds ≤100 km/hr -- 2.5 secs where design speed is ≥ 100 km/hr and access is controlled. -- 1.15m Passenger Car. -- 1.8m Commercial Vehicle.

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CREST

Section 2 - Road Geometry

Eye height (1.15m) Object height (0.2m)

Sight Distance

SAG Eye height (1.8m) Tail - light height (0.6m)

Bridge

Vertical Clearance

Sight Distance

SIGHT DISTANCE COMPONENTS

Figure 2.1.1

Table 2.1.1

Stopping Sight Distances on Level Bituminous or Concrete Surfaces. DISTANCE (m) TRAVELLED DURING* TOTAL STOPPING DISTANCE (m)

REACTION TIME Rr DESIGN SPEED (km/h) V 50 60 70 80 90 100 110 120 130

CO-EFFICIENT OF LONGITUDINAL FRICTION DEMAND fl 0.50 0.47 0.45 0.43 0.41 0.39 0.37 0.35 0.33

BRAKING 1.5 Secs

2.5 Secs

20 25 30 35 40 45

70 75 85 90

1.5 Secs 25 35 50 65 80 105 135 165 210

45 60 80 100 120 150

2.5 Secs

175 210 250 300

Total Distances given are approximately 5m to 8m longer than calculated distances to provide extra distance for stationary between vehicle and object.

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2.1.5

Section 2 - Road Geometry

Effect of Distance

Grade

on

terrain and cost of construction. It is an essential safety measure and to a large degree will influence both the location and design of a road. In undulating or flat country, it should occur frequently or continuously; at other locations minor modifications to alignment or grading may provide the sight distance necessary at little or no additional cost. As a general rule if overtaking sight distance cannot be economically provided at least once in each 2km of road, (depending on road type and volume), consideration should be given to the installation of auxiliary lanes in accordance with Section 8.1.

Braking

The distance a vehicle travels while being braked is longer on downhill grades and shorter on uphill grades. The braking distance component of the stopping sight distance formula (Section 2.1.4) when adjusted to take into account the effect of grade is :-

d=

V2 254( f l ±0.01G )

Where: d = braking distance (m). V = speed (km/h). fl = assumed coefficient of longitudinal friction demand for design speed (see Table 2.1.1). G = longitudinal grade per cent (+ uphill, - downhill)

(ii)

Isolated sections of roadway that have only minimum overtaking sight distance, are of little value if oncoming traffic prevents the utilisation of any overtaking opportunity provided. After overtaking sight distance has been established, it needs to be maintained continuously along a length of roadway to maximise overtaking opportunities and to enable an overtaking manoeuvre, once commenced, to be either completed or abandoned with safety. This length should be as long as economically practicable, and on roads with high traffic volumes should be equal to at least half the overtaking sight distance for the design speed.

2.1.6 Overtaking Sight Distance Overtaking sight distance is measured along the line of travel between two points each 1.15m above the road pavement. It is equal in length to the minimum distance between two opposing vehicles which will permit a safe overtaking manoeuvre. The overtaking sight distance figures for various speeds are shown in Table 2.1.2.

(iii)

50 60 70 80 90 100 110 120 130

Vertical alignment

The provision of minimum overtaking sight distance at crests is usually uneconomical and may not be used since many drivers are reluctant to overtake in these circumstances. Shorter crest curves with stopping sight distance often result in longer sections with overtaking sight distance.

Table 2.1.2 Overtaking Sight Distances DESIGN SPEED (km/h)

Length of continuing overtaking sight distance

OVERTAKING SIGHT DISTANCE (m) 1.15m-1.15m 250 300 350 450 600 750 900 1100 1400

(iv)

Auxiliary lane option

The provision of overtaking sight distance at some locations on two lane roads may not be cost effective and in these cases, a section of auxiliary lane construction with stopping sight distance is generally more economical than two lanes with overtaking sight distance.

When applying the overtaking sight distances given in Table 2.1.2, the following factors should also be considered : (i)

Frequency

The frequency at which overtaking sight distance should be provided is related to the travel speed, traffic volume, traffic composition, Road Design Guide

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RTA of NSW

Section 2 - Road Geometry

2.1.7 Intermediate Sight Distance

Table 2.1.4 Sight Distances on Level

Cases occur where it is not economically practicable to provide overtaking sight distance at reasonable intervals. The model for overtaking sight distance is based on one set of conditions, that is, the overtaking of a vehicle travelling at a lesser speed than the general travel speed on the section of road. In practice there is a wide range of conditions where a sight distance shorter than overtaking sight distance would be useful. For example, a much shorter sight distance is suitable to overtake a slowmoving truck.

DESIGN SPEED (km/h)

50 60 70 80 90 100 110 120 130

Where overtaking sight distance cannot be obtained and the introduction of an auxiliary lane is not warranted, the provision of intermediate sight distance may meet some overtaking needs by providing sight distance sufficient to complete or abort an overtaking manoeuvre before reaching an opposing vehicle which is just out of sight and travelling towards the first vehicle at the 85th percentile speed .

Bituminous or Concrete Pavements OVERSTOPPING INTERTAKING SIGHT MEDIATE SIGHT DISTANCE SIGHT (m) DISTANCE DISTANCE (m) (m) 45 140 250 60 180 300 80 220 350 100 260 450 120 300 600 150/175 380 750 210 450 900 250 530 1100 300 600 1400

2.1.9 Sight Distance at Night Unless roadway lighting is installed, sight distance at night is confined to the range of a vehicle's headlight beam. The distance of a driver's visibility is therefore limited regardless of which standard sight distance has been incorporated into the road's horizontal and vertical alignments for daylight driving. The limitations of vehicle headlights restrict the sight distance that can be safely assumed for visibility of an object on a roadway, to between 120m and 150m.This corresponds to satisfactory stopping distance up to 100km/h on a sealed road and less for a gravel surface.

The intermediate sight distances for various speeds are shown in Table 2.1.3

Table 2.1.3

Intermediate Sight Distances. DESIGN SPEED INTERMEDIATE (km/h) SIGHT DISTANCE (m) [1.15m-1.15m] 50 140 60 180 70 220 80 260 90 300 100 380 110 450 120 530 130 600

The criterion for headlight sight distance does not apply to roads which have street lighting to the standards prescribed by the S.A.A. Public Lighting Code, AS 1158, or on roads with high traffic volumes where it is necessary to keep headlights on dipped beam for a relatively high percentage of the travel time.

2.1.10

Sight Distance at Vertical Sags

Sag vertical curves may be designed to provide acceptable standards of comfort or to allow adequate headlight sight distance, with the latter usually being the governing criterion.

2.1.8 Summary of Sight Distances Table 2.1.4. summarises the sight distances as discussed for level bituminous or concrete pavements.

Where a sag vertical curve is on a straight, Figure 2.3.7 (page 2-37) gives the length of vertical curve which provides for headlight sight distance (to a maximum of 150m) with an angle of beam 1°above the horizontal axis.

2.1.11

Sight Distance at Vertical Crests

The minimum sight distance to be provided at vertical crests is stopping sight distance for the specified design speed and an object height of 0.2m. The provision of overtaking sight distance at vertical crests is usually uneconomical and a 4

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Section 2 - Road Geometry

0.3m under the sight line to allow for obstructions such as small boulders and grass growth.

more satisfactory option is the adoption of intermediate sight distance. Figures 2.3.3 and 2.3.4 (pages 2-33 & 2-34) give the length of vertical curve required to obtain stopping sight distance for eye height of 1.15m to zero pavement level and to an object height of of 0.2m for given design speeds and algebraic differences in grade.

Where a horizontal and crest vertical curve overlap, the line of sight between approaching vehicles may not be over the top of the crest but to one side and in part may be off the formation. Cutting down the crest on the pavement will not increase visibility if the line of sight is clear of the pavement, and the bottom of the bench may be lower than the shoulder level. In these cases, as well as in the case of sharp horizontal curves, a better solution may be to use a larger radius curve so that the line of sight remains within the formation. This will increase the 85th percentile speed and an iteration is necessary to ensure that stopping sight distance requirements are met.

Figures 2.3.5 and 2.3.6 (pages 2-35 & 2-36) give the length of vertical curve required to obtain overtaking and intermediate sight distances (1.15m to 1.15m) for given design speeds and algebraic differences in grade.

2.1.12

Sight Distance Curves

at

Horizontal

Where an obstruction off the pavement (such as a bridge pier, building, batter or natural growth) restricts sight distance, the minimum radius of curvature is determined by the stopping sight distance for the adopted design speed. On twolane, two-way roads however, it is preferable to provide for intermediate sight distance so as to minimise the use of barrier lines.

2.1.14

Where sag and crest vertical curves are combined with horizontal curves, the sight distance requirements of Sections 2.1.10, 2.1.11 & 2.1.12 should be amalgamated to ensure continuous provison of the appropriate sight distance.

The relation of a drivers line of sight to the sight distance measured around the curve and the curve radius is shown as Figure 2.2.6 (page 226). Also shown are the formulae to calculate the offset distance required from the pavement centreline to the line of sight obstruction and the minimum radius which avoids benching. Table 2.2.2 gives calculated offsets for stopping and intermediate sight distances for various curve radii.

2.1.13

2.1.15

Sight Distance at Intersections

(To be read in conjunction with Section 4.3.2) At all intersections, the following sight distance requirements should be satisfied: (i) Stopping sight distance (1.15m to zero), should be available on each approach of the intersection, so that drivers may appreciate the layout of the intersection by having clear visibility to pavement markings and channel?isation.

Benching for Visibility on Horizontal Curves

Benching is the widening of the inside of a cutting on a curve to obtain the specified sight distance. It usually takes the form of a flat table or bench over which a driver can see an approaching vehicle or an object on the road. In plan view, the benching is fixed by the envelope formed by the lines of sight. The driver and the object being approached are assumed to be in the inner lane. The sight distance is measured around a line 1.5m from the driver's side of the lane line and is the path the vehicle would follow in braking. Benching adequate for inner lane traffic satisfies visibility requirements for the outer lane (see Section 2.1.12).

(ii) A driver stopped in the minor road should have sufficient sight distance (1.15m to 1.15m) to react to an acceptable gap, start up and enter or cross the major traffic stream, without causing major disruption. (iii) Vehicles in the major road should have sufficient sight distance (1.15m to 1.15m) to observe a vehicle from the minor road move into the intersection, and in the event of a stall, be able to decelerate to a stop prior to collision. This sight distance is numerically equal to: • the distance travelled during the observation time (3 secs) plus,

Where sight benches in cuttings are required on horizontal curves or on combinations of horizontal and vertical curves, the extent of sight benching is best obtained graphically. The level of the sight bench should be fixed at least Road Design Guide

Sight Distance at Combined Horizontal & Vertical Curves

• the stopping distance of the vehicles on the major road (see Section 4.3.2).

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2.1.16

Sight Distance Roads

Section 2 - Road Geometry

on

2.1.20

Undivided

There are other minor constraints on sight distance that must be kept in mind by the designer:

The minimum sight distance to be provided at all points in a two-lane or multi-lane road is stopping distance.

• In avenues of trees, visibility can be curtailed at a sag owing to the line of sight being interrupted by the foliage. The same may happen where a bridge crosses a sag and the line of sight is cut by the structure.

Where barrier lines are to be avoided and cost associated with heavy earthworks is not a primary consideration, intermediate sight distance may be used. It satisfies many overtaking requirements though it does not comply with all the requirements assumed for overtaking sight distance.

• Guard fencing, bridge handrails, median kerbs and similar obstructions can restrict the visibility available at horizontal and vertical curves.

In undulating country where overtaking opportunities are few, and auxiliary lanes for overtaking are inappropriate, consideration should be given to providing intermediate sight distance at regular intervals.

• There is a considerable difference between the sight distance available to a driver depending on whether the curve ahead is to the left or to the right.

In cases where barrier lines are necessary at crests, shoulders should be wide enough for a stationary vehicle to stand well clear of the pavement, so that moving vehicles are not forced to cross the centreline of the road (see Section 3).

2.1.21

Effect of No-Overtaking Zone Markings

Reference is made the Department's publication, "Interim Guide to Signs and Markings", Section 7.4, for the practices of marking no-overtaking zones on two lane roads.

Care should be taken to avoid dips in the roadway which could hide an opposing vehicle and cause an overtaking driver an unexpected hazard.

2.1.17

Other Restrictions to Visibility

Sight Distance on Divided Roads

At least stopping sight distance is to be provided at all points on a divided road. Generally intermediate sight distance should be adopted where economically practicable.

2.1.18

Sight Distance Underpasses

through

Where economically feasible, overtaking sight distance should be maintained as the highway passes under a structure. If this cannot be achieved, intermediate sight distance will suffice. The absolute minimum sight distance which must be provided at underpasses is stopping sight distance.

2.1.19

Sight Distance at Interchanges

Mutual sight must be available between the drivers of converging vehicles at interchanges. This is particularly important at the merge of onload ramps and beneath grade separations where piers or abutment walls may obscure visibility.

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Section 2 - Road Geometry

In flat country, long straights on roads may have to be accepted. If curves are deliberately introduced into the design to break the monotony, they

2.2 HORIZONTAL ALIGNMENT (To be read in conjunction with Section )6

2.2.1 General

should have long arc lengths or else they will look like kinks. Unless the change in alignment is considerable, oncoming headlights will remain a nuisance to drivers.

The speed adopted on an open road is affected more by the driver's perception of the horizontal alignment of the road than by any other single design feature. For this reason, whenever curves are used to change the direction of travel or to suit the topography, the radii must be large enough to permit travel speeds commensurate with those expected on adjoining straights or along the whole of the section being designed. Generally, the adopted alignment should be as direct as possible, with curve radii as large as practicable.

2.2.3 Curved Alignment The second element of horizontal alignment is the curve. Properly designed curves are appreciated by drivers because they provide interest by presenting a changing panorama while arousing a sense of anticipation of what is beyond the curve. The most advantageous property of a curving roadway is that it provides a visual appreciation of the driver's position and speed in relation to roadside objects and other traffic.

An alignment without straight sections is described as curvilinear. Curvilinear alignment is suitable for dual carriageway roads but is undesirable for two-lane, two-way roads, as it does not provide sufficient length for overtaking.

It is preferable that the radii of horizontal curves be the largest attainable. Isolated small radii curves in an otherwise free flowing horizontal alignment and small radii curves at the end of long straights, on steep down grades and over crests are unsafe and must be avoided. General details of curve elements are given in Tables 2.2.2 and 2.2.3

As with other elements of design, horizontal alignment should generally provide for safe and continuous operation at a uniform travel speed. Sudden reductions in standard, such as isolated curves of small radius (particularly at the end of long straights), introduce an element of surprise to the driver and should be avoided.

2.2.4 Horizontal Curve Radius

Where physical restrictions on curve radius cannot be overcome and it becomes necessary to introduce curvature of lower standard than the design speed of the project, the design speed of successive geometric elements should not change by more than 10km/h (on two way roads both directions of travel need to be considered).

For a given speed, and under normal conditions, the radius for a horizontal curve should not be less than the range quoted in Table 2.2.1

Table 2.2.1

Minimum Radii for Horizontal Curves Design Speed Radii (km/h) (m) 50 50 or more 60 90 or more 70 150 or more 80 240 or more 90 340 or more 100 460 or more 110 600 or more 120 800 or more 130 1000 or more

2.2.2 Straight Alignment The tangent or straight section is the most common element of horizontal alignment. It provides clear orientation, but at the same time is visually uninteresting unless aimed at some landmark. Being totally predictable, with a view which appears static, it causes driver monotony and encourages the undesirable combination of fatigue and excessive speed. At night, opposing headlights can cause problems.

Accident records suggest that curves with radii between 300m and 440m should be avoided for design speeds greater than 70km/h. They are deceptive to the driver as it appears that they can be safely travelled at higher speeds than is actually possible. Wherever possible, curves are to be selected to give stopping sight distance for the adopted design speed, with the line of sight contained within the formation (see Section 2.2.24).

Straights of suitable length are desirable on two lane roads to facilitate overtaking manoeuvres and should be provided as frequently as the terrain permits. Straights are too long if they encourage drivers to travel well in excess of the design speed and should therefore be avoided. Straights which are too short to provide adequate separation between adjoining curves, should also be avoided. Road Design Guide

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2

June, 95 Issue 1.0

NOTES:

130

130

120

110

100

80

80

70

%

470

470

400

340

280

230

3#

3

4

5

6

6

7

7

140

180

7

E

100

Lh

(m)

Curve Super TS-TS

A*

3#

0.3

0.3

0.4

0.4

0.4

0.5

0.6

0.6

80#

80

80

80

80 60

60

60

80

40

40

80

B*

0.3

0.4

0.5

0.4

0.6

0.5#

0.5

0.6

0.7

0.7

0.7

0.8

0.9

0.9

90#

90

90

90

90

90

90

80

80

60

60

60

60

60

0.3

0.4

0.6

0.8

1.3

Plan Relative Super Plan C'line 2 C'line Trans. Offset Grade Trans Trans.2 Offset (m) % (m) (m) (m) (m) Lp Gr Le Lp S S

60

60

Relative Super Grade Trans % (m) Gr Le

0.6#

0.6

0.7

0.8

0.9

0.9

1.0

1.2

1.3

110#

110

110

110

110

110

110

90

80

80

80

80

80

80

60

60

0.3

0.4

0.5

0.7

0.9

0.8

1.3

Relative Super Plan C'line Grade Trans. Trans.2 Offset % (m) (m) (m) Le Lp Gr S

C*

HORIZONTAL ALIGNMENT

For design speeds grater than 70 km/h, curve radii within the shaded box are only to be used in exceptional circumstances. A Plan transition (Lp) is not required if the calculated maximum offset (S) from the base control line is less than 300mm. Lane widening is not required if the calculated widening is less than 200mm. Adoption of 2.8, 3.0 and 3.25m lane widths is not recommended for design speeds of 80, 90 and 100 km/h respectively. S.S.D, I.S.D, O.S.D = Stopping, Intermediate and Overtaking Sight Distances. Use is optional. For transition and widening offsets, see Table 2.2.3.

R 90 100 110 120 130 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 500 550 600 650 700 750 800 900 1000 2000 3000 over 3000

V

1. 2. 3. 4. 5. # *

(m)

(km/h)

60

Curve Radius

Speed

Table 2.2.2 Pavement Widening 3

0.3

0.3

0.4

0.4

0.4

0.4

0.5

0.6

0.7

0.2

0.2

0.3

0.3

0.3

0.3

0.4

0.5

0.6

4

0.2

0.3

0.4

3.5

0.2

0.3

3.7

Benching Offset

300

600

1400

(m) (m) S.S.D. I.S.D. O.S.D. S.S.D. I.S.D. 6.6 43.5 6.1 39.9 180 60 300 5.7 36.8 5.3 34.1 5.0 31.8 4.8 29.8 6.6 38.2 80 220 350 6.0 34.4 5.6 31.2 5.2 28.6 6.8 36.1 6.4 33.5 450 6.0 31.3 100 260 5.7 29.4 5.5 27.7 6.8 34.2 6.5 32.5 200 120 6.3 30.9 600 6.0 29.4 5.8 28.1 5.6 26.9 7.7 40.3 380 750 7.2 37.3 150 6.7 34.1 10.7 43.3 10.0 40.2 450 900 210 9.4 37.5 12.0 48.0 530 1100 11.3 45.1 250 10.2 40.3 12.8 46.3 300 600 1400 7.2 24.0 5.3 16.5

Sight Distances 5

A Normal two-lane roadway with control on centreline. B Two-lane roadway with control along one edge. Four-lane roadway with control on centreline. Two-lane roadway with climbing lane and control on the centreline of the basic two lanes. C Multi-lane roadway with more than two lanes between the control and the edge of the travelled way.

0.5

0.5

0.6

0.6

0.6

0.7

0.7

0.8

0.9

2.8

(m) of 3.0 3.25

for Nominal Lane Width

RTA of NSW Section 2 - Road Geometry

Road Design Guide

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3 TRANSITION AND WIDENING OFFSETS TYPE A

(Control other than centreline of normal two-lane roadway, refer Table 2.2.2)

Radius 90m - 140m

SS

Distances from SS Super Transition

Crossfall %

Outside of Control Inside of Control

TS

10

0

-3.0

-2.7

10 -1.3

-3.0

-3.0

-3.0

20

Plan Transition and Widening

Widening Per Lane

Nominal Width

3.7*

Radius 160m - 220m

SS

Distances from SS Super Transition

Crossfall %

Outside of Control Inside of Control

Widening Per Lane

Nominal Width

Crossfall %

Widening Per Lane

-5.7

-6.7

-7.0

.56 .67 .53

.60 .90

0 0

.30 .45 .35 .30

0

.07

-3.0

-2.7

-1.3

-3.0

-3.0

-3.0

0.3 -3.0

10

0

.20 .15

Crossfall %

Widening Per Lane

5.3

-3.3

-4.3

-5.7

.20 .40 .30 .25

.37 .60 .45

0 0

.03 .20 .15 .12 .07

0

.05

.15 .10

20

30

40

50

60

70

80

90

.38 .23 .15

-6.7 .40 .80 .60 .50

70 7.0 -7.0

.30 .20

TP

SC

-2.7 -1.8

-0.5

0.8

2.0

3.3

4.5

5.8

6.7

7.0

-3.0

-3.0

-3.0

-3.0

-3.3

-4.5

-5.8

-6.7

-7.0

0 0 0

.01 .12 .08

-3.0 .07 .23

.43 .47

.49 .58 .42

.50 .70 .50

0 0

.07 .03

.25 .35 .25 .20 .10

.33 .17

.40 .20

-3.0

.17 .13 .07

.33 .27 .13

Widening Not Required

SS

Nominal Width

SC

3.7

10

0

SC

20

30

40

TP 50

60

70

TS 10

90

-3.0

-2.8 -1.9

-0.8

0.4

1.5

2.6

3.7

4.9

80 5.8

6.0

-3.0 -3.0

-3.0 -3.0

-3.0

-3.0 -3.0 .06 .01 .23 .12 .13 .07 .10 .05

-3.2 .20 .35

-3.9

-4.9

-5.8

-6.0

.34 .39 .47 .58 .27 .33 .20 .15 .20 .25 Widening Not Required

.40 .70

Offset to True Control Plan Transition and Widening

60 6.7

-3.0

Radius 340m - 440m

Super Transition

.30

50

3.7*

Outside of Control Inside of Control

.40

40

2.8 3.0 3.25 3.5

Distances from SS

.70 .60

.23

TP

TS 10

.45 .30

70

30 2.0

0 0 0

SS

Nominal Width

-4.3

.04 .22 .17 .15 .10

TS

Offset to True Control Plan Transition and Widening

-3.3

20

Radius 240m - 320m Super Transition

7.0

10

3.7*

Outside of Control Inside of Control

60 6.7

0

2.8 3.0 3.25 3.5

Distances from SS

50 5.3

10

Offset to True Control Plan Transition and Widening

40 3.7

0 0 0

2.8 3.0 3.25 3.5

SC

30 2.0

0.3 -3.0

Offset to True Control

TP

0 0 0 0

2.8 3.0 3.25 3.5

.40 .30

3.7* * To be used in exceptional circumstances only

Road Design Guide

June, 95 Issue 1.0

3

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3

TYPE A

(Continued) (Control other than centreline of normal two-lane roadway, refer Table 2.2.2)

Radius 460m - 550m

SS

Distances from SS Outside of Control Inside of Control

Crossfall %

Super Transition

10

TS

0

10

30

40

50

60

70

80

90

-3.0

-2.8 -1.9

-0.8

0.4

1.5

2.6

3.7

4.9

5.8

6.0

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 .06 .01 .23 .12 .13 .07 .10 .05

-3.2 .20 .35

-3.9

-4.9

-5.8

-6.0

.39 .34 .58 .47 .27 .33 .20 .15 .25 .20 Widening Not Required

.40 .70 .40 .30

-3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

SC

TP

20

0 0 0 0

2.8 3.0 3.25 3.5 3.7*

Radius 600m - 700m SS Distances from SS Super Transition

Crossfall %

Widening Per Lane

Nominal Width

TP 50

60

70

1.0

2.0

3.0

4.0

20

-3.0

-2.8 -2.0

-1.0

0.0

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 -3.0 -3.3 -4.0 Offset Not Required .30 .20 .10 .50 .40 .13 .20 .07 .27 .33 .10 .05 .15 .20 .25 Widening Not Required

0

10 -3.0

Offset to True Control Plan Transition and Widening

SC

40

30

10

Outside of Control Inside of Control

TS

2.8 3.0 3.25 3.5

0 0 0

90

80 4.8

5.0

-4.8

-5.0

.60 .40 .30

3.7*

Radius 750m - 900m

SS

Distances from SS Super Transition

Widening Per Lane

Nominal Width

60

70

0.5

1.4

2.2

20

80

90

-3.0

-2.8 -2.1

-1.2

-0.4

3.1

3.8

4.0

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 -3.0 -3.2 -3.5 Offset Not Required .30 .20 .10 .40 .50 .13 .20 .07 .27 .33 .10 .15 .05 .25 .20 Widening Not Required

-3.8

-4.0

0

10 -3.0

Offset to True Control Plan Transition and Widening

TP 50

30

10

Outside of Control Inside of Control

Crossfall %

SC

40

TS

2.8 3.0 3.25 3.5

0 0 0

.60 .40 .30

3.7*

Radius 1000m - 3000m SS Distances from SS Super Transition

Crossfall %

20

30

40

-3.0

-2.8 -2.3

-1.5

-0.8

0.0

0.8

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 -3.0 -3.0 -3.0 Offset Not Required .08 .17 .25 .42 .33 .05 .10 .15 .20 .25 .03 .07 .10 .13 .17 Widening Not Required

10

Outside of Control Inside of Control

0

10 -3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

SC

TP 50

TS

2.8 3.0 3.25 3.5 3.7*

0 0 0

60

70

1.5

2.3

90

80 2.8

3.0

-3.0

-3.0

.50 .30 .20

* To be used in exceptional circumstances only

4

June, 95 Issue 1.0

Road Design Guide

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3

TYPE B

(Continued) (Control other than centreline of normal two-lane roadway, refer Table 2.2.2)

Radius 90m - 140m 5.3Distances from SS Super Transition

Crossfall %

TS

SS

Outside of Control Inside of Control

10

0

-3.0

-2.7

10 -1.8

-3.0

-3.0

-3.0

20

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

3.7*

Radius 160m - 220m

SS

Super Transition

Crossfall %

Outside of Control Inside of Control

Widening Per Lane

Nominal Width

Super Transition

Crossfall %

0 0

.19 .30 .23 .20

0

.05

Widening Per Lane

Nominal Width

90

6.7

7.0

-5.8

-6.7

-7.0

1.11 1.27 .60 .75 .47 .58

1.30 .90

70 5.8

-3.3

-4.5

.65 .45 .35 .30 .20

.40 .27

.50 .33

.15

.20

.25

.30

60 4.5

70 5.8

80 6.7

90

-4.5 .68 .53 .40 .33

-5.8 .78 .67 .50 .42

-6.7 .80 .80 .60 .50

-7.0

.20

.25

.30

.13

.17

.20

6.7

TP 50

2.0

3.3

-3.0

-3.0

-3.3

.12 .27 .20 .17

.40 .40 .30

0 0

.02 .13 .10 .08 .05

0

.03

.10 .07

20

30

40

50

60

70

-2.7

-1.8

-3.0

-3.0

-3.0

-0.5 -3.0 0 0 0

TS

.25 .15 .10

TP

SC

-2.7 -1.9

-0.8

0.3

1.4

2.5

3.7

4.8

-3.0

-3.0

-3.0

-3.0 0 0 0

-3.0

-3.1

-3.7

-4.8

-5.9

-6.7 -7.0

.51 .47 .33

.59 .58 .42

.60 .70 .50

.27 .13

.33 .17

.40 .20

10 -3.0

2.8 3.0 3.25 3.5 3.7*

0 0

.01 .12 .08 .07 .03

.09 .23 .17 .13 .07

.30 .35 .25 .20 .10

Super Transition

Widening Per Lane

Nominal Width

100 7.0

10

0

10

SC

TP

TS

100

20

30

40

50

60

70

80

90

-3.0

-2.8 -2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

5.8

6.0

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0 .01 .12 .07 .05

-3.0 .06 .23

-3.2

-4.0 .34 .47

-5.0

-5.8

-6.0

.39 .58

.40 .70

.33 .25

.40 .30

-3.0

Offset to True Control Plan Transition and Widening

90

Widening Not Required

SS Outside of Control Inside of Control

7.0

-3.0

0

Radius 340m - 440m

Crossfall %

.40

80 5.9

10

Distances from SS

.70 .60

SC

40

-3.0

SS

80

60 4.5

30 0.8

20

Offset to True Control Plan Transition and Widening

.13 .10

TS 10

Radius 240m - 320m Outside of Control Inside of Control

-3.0

.03 .15 .12 .10 .07

0

2.8 3.0 3.25 3.5 3.7*

Distances from SS

-3.0

10

Offset to True Control Plan Transition and Widening

50 3.3

0 0 0

2.8 3.0 3.25 3.5

Distances from SS

40 2.0

-0.5 -3.0

SC

TP 30 0.8

0 0 0 0

2.8 3.0 3.25 3.5 3.7*

.20 .35 .20 .13 .27 .10 .15 .20 Widening Not Required

* To be used in exceptional circumstances only

Road Design Guide

June, 95 Issue 1.0

5

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3

TYPE B

(Continued) (Control other than centreline of normal two-lane roadway, refer Table 2.2.2)

Radius 460m - 550m

SS

Distances from SS Outside of Control Inside of Control

Crossfall %

Super Transition

10

0

TS 10

30

40

50

TP 60

70

80

90

Widening Per Lane

Nominal Width

100

-3.0

-2.8 -2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

5.8

6.0

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0 .01 .10 .07 .05

-3.0 .04 .20

-3.2

-4.0

-5.0

-5.8

-6.0

.26 .15 .40 .30 .20 .27 .13 .10 .20 .15 Widening Not Required

.29 .50 .33 .25

.30 .60

-3.0

Offset to True Control Plan Transition and Widening

SC

20

0 0 0 0

2.8 3.0 3.25 3.5

.40 .30

3.7*

Radius 600m - 700m

SS

Distances from SS Outside of Control Inside of Control

Crossfall %

Super Transition

10

0

10

20

40

50

0.3

0.6

1.4

-3.0

-2.8 -2.1

-1.2

-3.0 -3.0

-3.0

-3.0 -3.0

-3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

TP

TS 30

2.8 3.0 3.25 3.5

0 0 0

60 2.3

70 3.2

-3.0 -3.0 -3.0 -3.3 Offset Not Required .30 .20 .10 .40 .13 .07 .20 .27 .15 .10 .05 .20

80 4.1

SC 90 4.8

100 5.0

-4.1 -4.8

-5.0

.50 .33 .25

.60 .40 .30

Widening Not Required

3.7*

Radius 750m - 900m

SS

Distances from SS Outside of Control Inside of Control

Crossfall %

Super Transition

10

0

10

20

TS 30

40

50

TP 60

70

0.1

0.9

1.7

2.4

-3.0

-2.8 -2.2

-1.4

-0.7

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 -3.0 -3.0 -3.2 Offset Not Required .40 .30 .10 .20 0 .07 0 .27 .13 .20 .10 .15 .05 0 .20 Widening Not Required

-3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

2.8 3.0 3.25 3.5

80 3.2

SC 90

100

3.8

4.0

-3.5

-3.8

-4.0

.50

.60

.33 .25

.40 .30

3.7*

Radius 1000m - 3000m

SS

Distances from SS Super Transition

Crossfall %

20

30

40

-3.0

-2.8 -2.3

-1.7

-1.0

-0.3

0.3

-3.0 -3.0

-3.0 -3.0

-3.0

-3.0

-3.0 -3.0 -3.0 -3.0 Offset Not Required .17 .25 .33 .08 .10 .15 .20 .05 .07 .10 .03 .13 Widening Not Required

10

Outside of Control Inside of Control

0

10

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

SC

TP 50

TS

2.8 3.0 3.25 3.5

0 0 0

60

70

1.0

1.7

80 2.3

90 2.8

100

-3.0

-3.0

-3.0

.42 .25 .17

.50 .30

3.0

.20

3.7* * To be used in exceptional circumstances only

6

June, 95 Issue 1.0

Road Design Guide

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3

TYPE C

(Continued) (Control on multilane road, refer Table 2.2.2)

Radius 90m - 140m

SS

Distances from SS Crossfall %

Super Transition

Outside of Control Inside of Control

0

10

20

30

40

-3.0

-2.7

-1.8

0.8

2.0

-3.0

-3.0

-3.0

-0.5 -3.0

50 3.3

-3.0

-3.0

0 0

.03 .15 .12 .10 .07

0

.05

20 -0.8 -3.0

30 0.3 -3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

0 0 0

2.8 3.0 3.25 3.5 3.7*

Radius 160m - 220m

SS

Distances from SS Super Transition

Crossfall %

Outside of Control Inside of Control

0

-3.0

-2.7

10 -1.9

-3.0

-3.0

-3.0

0 0 0

Widening Per Lane

Nominal Width

2.8 3.0 3.25 3.5

0 0 0

3.7*

Radius 240m - 320m

SS

Distances from SS Super Transition

Crossfall %

Outside of Control Inside of Control

10 -3.0

0 10 -2.8 -2.1

-3.0

-3.0

Widening Per Lane

Nominal Width

Crossfall %

Widening Per Lane

.15

40 1.4

50 2.5

-3.0 .02 .13 .10 .08 .05 .05

.27 .20

-6.7

-7.0

1.27 .75 .58

1.30 .90

.50 .33

.70 .60 .40

.25

.30

60

70

80

3.7

4.8

5.9

-3.1

-3.7

-4.8

-5.9

.12 .27 .20 .17 .10

.40 .40 .30 .25 .15

.68 .53 .40 .33

.78 .67 .50

.07

.10

TP

SC

.20 .13

.42 .25 .17

90 6.7

100 7.0

-6.7 .80 .80 .60 .50

-7.0

.30 .20

SC

TP 80

-1.2

70 3.4

4.3

5.2

-3.0

-3.0

-3.0

-3.0

-3.1

-3.5

-4.3

-5.2

0 0 0

.01 .09 .06

.06 .17 .12

.19 .26 .19

.05

.10

0

.02

.05

.15 .07

.71 .44 .31 .25 .13

.84 .53

0

.45 .35 .25 .20

-3.0

SS

Nominal Width

.10

-5.8

60 2.5

TS

.10

90

.38 .30 .15

100 110 120 6.1 6.8 7.0 -6.1 -6.8 -7.0 .89 .90 .61 .70 .44 .50 .35 .40 .18

.20

SC

1.1

-2.8 -2.2

-1.4

-0.5

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0

-3.0

-3.0

0 0 0 0

.01 .09 .05 .04

.05 .17 .10 .07

.15 .26 .15 .11

10 -3.0

2.8 3.0 3.25 3.5

30

60 1.9

-3.0

0

20

TP 50

40 0.3

10

Offset to True Control Plan Transition and Widening

.19 .30 .23 .20 .13

1.11 .60 .47 .40

Widening Not Required

Radius 340m - 440m

Super Transition

-4.5

.65 .45 .35 .30 .20

90 7.0

50 1.5

3.7*

Outside of Control Inside of Control

-3.3

80 6.7

5.8

40 0.6

2.8 3.0 3.25 3.5

Distances from SS

70

TS 30 -0.3

20

Offset to True Control Plan Transition and Widening

SC 60 4.5

TS

10

Offset to True Control Plan Transition and Widening

TP

TS

10

70 2.7 -3.1 .35 .35 .20 .15

80 3.5 -3.6 .55 .44 .25 .19

90 4.4

100 110 120 5.2 5.8 6.0

-4.4 -5.2 .65 .69 .53 .61 .30 .35 .23 .26

-5.8 -6.0 .70 .70 .40 .30

Widening Not Required

3.7* * To be used in exceptional circumstances only

Road Design Guide

June, 95 Issue 1.0

7

RTA of NSW

Section 2 - Road Geometry

TABLE 2.2.3

TYPE C

(Continued) (Control on multilane road, refer Table 2.2.2)

Radius 460m - 550m

SS

Distances from SS Super Transition

10

Outside of Control Inside of Control

Crossfall %

-3.0

0

TS

-2.8 -2.2

-3.0 -3.0 -3.0

20

30

-1.4 -3.0

10 -3.0

-0.5

40 0.3

-3.0

-3.0

0 0 0 0

.01 .07 .05 .04

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

2.8 3.0 3.25 3.5

TP 50

SC 70

80

90

1.1

60 1.9

2.7

3.5

4.4

-3.0

-3.0

-3.1

.03 .15 .10 .07

.11 .22 .15 .11

.25 .30 .20

-3.6 .39 .38

-4.4 .47 .45 .30

.15

.25 .19

.23

100 110 120 5.2 5.8 6.0 -5.2 .49 .53 .35 .26

-5.8 -6.0 .50 .60 .40 .30

Widening Not Required

3.7*

Radius 600m - 700m

SS

Distances from SS Crossfall %

Super Transition

Widening Per Lane

Nominal Width

SC

20

30

-2.8 -2.3

-1.5

-0.8

40 -0.1

0.6

60 1.4

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0

-3.0

-3.0

0 0 0 0

.01 .07 .05

.03 .15 .10

.08 .22 .15

0

10 -3.0

Offset to True Control Plan Transition and Widening

TP 50

-3.0

10

Outside of Control Inside of Control

TS

2.8 3.0 3.25 3.5

70 2.1 -3.0 .20 .30 .20

.04 .07 .15 .11 Widening Not Required

100 110 120 4.3 4.8 5.0

80 2.8

90 3.5

-3.1 .32 .38

-3.7 -4.3 .37 .39 .45 .53 .30 .35 .23 .26

.25 .19

-4.8 -5.0 .40 .60 .40 .30

3.7*

Radius 750m - 900m

SS

Distances from SS Super Transition

Widening Per Lane

Nominal Width

SC

20

-3.0

-2.8 -2.4

-1.7

-1.1

40 -0.5

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0

-3.0

-3.0

0 0

.01 .07

0 0

.02 .15 .10

.06 .22 .15

.05 .15 .04 .07 .11 Widening Not Required

0

10 -3.0

Offset to True Control Plan Transition and Widening

TP 50

30

10

Outside of Control Inside of Control

Crossfall %

TS

2.8 3.0 3.25 3.5

0.6

60 0.8

70

80

90

1.5

2.1

2.7

-3.0 .15

-3.0 .24 .38

-3.2 -3.6 .28 .29 .45 .53 .30 .35 .23 .26

.30 .20

.25 .19

100 110 120 3.4 3.8 4.0 -3.8 -4.0 .30 .60 .40 .30

3.7*

Radius 1000m - 3000m

SS

Distances from SS Super Transition

Crossfall %

20

30

-3.0

-2.8 -2.5

-1.9

-1.4

40 -0.8

-3.0 -3.0

-3.0

-3.0

-3.0

-3.0

10

Outside of Control Inside of Control

TS

0

10 -3.0

Offset to True Control Plan Transition and Widening

Widening Per Lane

Nominal Width

2.8 3.0 3.25 3.5 3.7*

0 0 0

TP 50

SC 70

80

90

0.8

1.4

1.9

100 110 120 2.5 2.8 3.0

-3.0 -3.0 -3.0 -3.0 Offset Not Required .25 .31 .12 .06 .19 .04 .15 .19 .07 .11 .05 .10 .02 .07 .13 Widening Not Required

-3.0

-3.0 -3.0 -3.0

-0.3

60 0.3

.38 .23 .15

.44 .50 .26 .30 .18 .20

* To be used in exceptional circumstances only

8

June, 95 Issue 1.0

Road Design Guide

RTA of NSW

Section 2 - Road Geometry

For a given radius and speed, a set force is required to maintain the vehicle in this path. In road design, this is provided by the transverse friction demand, developed between tyre and pavement, and by superelevation.

2.2.5 Length of Curved Roadway Length of curved roadway is the sum of the length of circular arc on the true control line and the lengths of the plan transitions which connect the shifted circular arc to the tangents, or the length of the pegged base control line if plan transitions are not required (see Section 2.2.19). The total length should provide a pleasing appearance by avoiding the impression of a "kink" in the horizontal alignment. Also, the shifted circular arc should be sufficiently long, in relation to the lengths of the spiral transitions, to avoid the appearance of a "hump" in the outer pavement edge due to superelevation.

For small values of superelevation, the following approximation may be accepted:

v2 V2 e+ f = or gR 127 R Where: e = pavement superelevation (m/m or tangent of angle). This is taken as positive if the pavement falls towards the centre of the curve f = assumed value of transverse friction demand between vehicle tyres and road pavement. (Table 2.24) Taken as positive if the frictional force on the vehicle acts towards the centre of the curve. g = acceleration due to gravity (9.8m/sec2) v = speed (m/sec) V = speed (km/h) R = radius (m)

The appropriate minimum length of curved roadway is a function of aesthetics and is therefore subjective. However, a convenient measure which satisfies this aesthetic function, is the adoption of a minimum length of at least three times the length of plan transition or desirably the distance travelled by a vehicle during one second for each 10 km/h of design speed. The latter is calculated with the following formula:

Lh =

Where f equals zero in the formula, the whole of the centripetal force is exerted by the superelevation. This condition can occur on large radius curves with positive superelevation or for slow moving vehicles on curves of any radius. At low speeds, f can be negative, and the curve is then over-superelevated for that speed. Curves are generally designed, so that a positive f is obtained for the range of vehicle speeds likely to occur.

V ×1000 V V 2 × = 3600 10 36

Where:

Lh = length of horizontal curve (m) V = design speed (km/h)

Appropriate lengths of curved roadway for various radius curves are given in Table 2.2.2.

Figure 2.2.1 illustrates the relationship of speed, radius and superelevation based on the assumed coefficients of transverse friction demand listed in Table 2.2.4.

2.2.6 Circular Arc The approximate length of circular arc on the base control line is the difference between the length of curved roadway and the sum of half the lengths of the plan transitions.

2.2.9 Transverse Friction The value of the transverse friction factor is a function of the type and condition of the road surface, the behaviour of the vehicle and the type and condition of the tyres. It is therefore variable and the least determinable of the elements adopted to determine the "safe speed" of a horizontal curve.

2.2.7 Deflection Angle The minimum deflection angle (∠°) required to contain the desirable length of pegged circular arc may be derived with the formula:

The upper limit of the transverse friction factor (friction supply) is the point of impending skid. As horizontal curves are designed to avoid skidding, with a margin of safety, the assumed transverse friction factor, (f) adopted for design purposes, (friction demand) is substantially less than this upper limit.

∠°=Length of Pegged Circular Arc 0.01745R

2.2.8

Vehicular Movement Circular Path

on

a

As a vehicle travels on a circular curve, a centripetal force must be applied to balance the inertial forces associated with the circular path. Road Design Guide

June, 95 Issue 1.0

9

10

%

E

June, 95 Issue 1.0

0

1

2

3

4

5

6

7

8

9

10

60

70 80 90 100 120

70 80

140 160 180 200

250

90

100

350

Speed (km / h)

300

Note: The grey boxed areas define the recommended "E" to be adopted for the ranges of radii indicated. For "E" less than 3%, adopt 3%.

50

60 400

110

500

(FOR SEALED RURAL ROADS)

Curve Radius (m)

SPEED / RADIUS / SUPERELEVATION RELATIONSHIP

120

600

130

800

700

140

1300

1200

1100

1000

f 0.30 0.24 0.19 0.16 0.13 0.12 0.12 0.11 0.11

Figure 2.2.1

900

V 50 60 70 80 90 100 110 120 130

RTA of NSW Section 2 - Road Geometry

Road Design Guide

RTA of NSW

Section 2 - Road Geometry

A driver's attitude, when driving, varies in relation to the road environment, terrain, surface conditions and the traffic density on the road. For instance, drivers will use higher values of transverse friction when traffic density is low and/or the road surface is dry, than when the opposite conditions apply.

Table 2.2.5 radius 50-330 330-550 550-750 750-950 >950

The maximum values of assumed transverse friction demand (f) to be adopted for the design of horizontal curves, for various conditions, are given in Table 2.2.4; they are a guide for average conditions and should be used cautiously.

2.2.12

Transverse Friction Demand BITUMEN AND CONCRETE PAVEMENTS 0.30 0.24 0.19 0.16 0.13 0.12 0.12 0.11 0.11

50 60 70 80 90 100 110 120 130

GRAVEL AND UNSURFACED ROADS* 0.14 0.13 0.12 0.11 0.10 -

Minimum Superelevation Values

The minimum value of superelevation should not be less than the slope of the normal crossfall adopted for the adjacent straight road alignment. This is normally 3% but can be 4% in flat country areas where near level longitudinal alignment is unavoidable.

Superelevation - General

In urban situations, although 3% is the recommended minimum superelevation, lower superelevation values may be adopted in difficult circumstances.

Horizontal curves are superelevated to balance the effects of centrifugal force. The amount of superelevation will depend on vehicle speed, curve radius and pavement surface characteristics. The rate to be adopted is chosen for the aspects of safety, comfort and appearance.

2.2.14

Adverse Crossfall

In rural situations all curves under 3000m radius should be superelevated. However, to improve pavement drainage on very flat longitudinal grades, or in the design of temporary roadways, sidetracks and temporary connections, consideration may be given to the use of up to 3% adverse crossfall.

Curves of 3000m radius and over may be superelevated but this is not generally necessary except for appearance reasons. Superelevation gives the curve a more natural appearance in certain situations, especially in flat open terrain, and helps define the outer edge of pavement

The curve radius with adverse crossfall can be calculated with the same formula used for positive crossfall (See Section 2.2.8). However the e value for superelevation is negative and the f value for the assumed transverse friction demand is 2/3 of the rural values listed in Table 2.2.4.

Desirable Superelevation

Values of desirable superelevation are shown in Table 2.2.5.

Road Design Guide

The maximum value of superelevation is limited by heavily laden or slow moving vehicles and by conditions of ice and snow. In rural areas the maximum value of superelevation to be adopted is 10% with the desirable maximum being 7%. In certain situations it may be desirable to increase the superelevation to the maximum as an additional safety feature. The development of a steep superelevation may create difficulties with drainage on the inside of a curve and it may be necessary to slightly increase the grade.

2.2.13

NOTE: Desirable of superelevation (Table 2.2.5) must not be reuced on the basis of assumed values of transverse friction demand.

2.2.11

Maximum Superelevation Values

In urban areas superelevation exceeding 4% is undesirable because of pedestrian traffic.

* extrapolated from 1945 D.M.R. Data Book

2.2.10

superelevation 7% 6% 5% 4% 3%

Figure 2.2.1 illustrates typical combinations of superelevation, curve radii and friction demand.

Table 2.2.4 Maximum Assumed Values of DESIGN SPEED (km/h)

Desirable Superelevation

June, 95 Issue 1.0

11

RTA of NSW

Section 2 - Road Geometry

In urban situations where drivers are more adaptable to changes in radius, superelevation and transverse friction, the use of adverse crossfall on small radii curves is tolerable.

2.2.15

2.2.16

Superelevation on Steep Grades

The adoption of the maximum values of super?elevation on very steep grades may increase the longitudinal grade on the outer lanes unacceptably . Usually the superelevation is the only geometric element which can be varied and it sometimes becomes necessary to either reduce the superelevation or extend the length of the eases at the end of the superelevation development .

Superelevation on Bridges

Where a bridge structure is proposed near a horizontal curve and intrusion of the normal application of the superelevation transition onto the deck is unavoidable, it is preferable to maintain a uniform section on the bridge deck by continuing the rate of curve superelevation along the full length of the bridge.

It is recommended that designers profile the outer edges of pavement to ensure acceptable drainage design and aesthetics.

Superelevation Development L e Plan Transition L p 20m Ease (min) Outer Edge of Pavement 20m Ease (min)

E Relative grade

Control

Axis

n

of

Rotation E

20m Ease (min) 20m Ease (min)

Inner Edge of Pavement

Not to Scale S.S. Notes 1. 2. 3. 4. 5. 6. 7. 8.

T.S.

T.P.

S.C.

T.S. = Tangent Spiral, common point of tangent and spiral. T.P. = Tangent Point, common point of tangent and curve S.S. = Start of Superelevation Transition. S.C. = Spiral Curve, common point of spiral and circular curve n = Normal crossfall (%) E = Superelevation (%) All longitudinal measurements are made along the pegged control line. All lateral measurements are made at right angles to pegged control line.

SUPERELEVATION PROFILES Figure 2.2.2

12

June, 95 Issue 1.0

Road Design Guide

RTA of NSW

2.2.17

Section 2 - Road Geometry

(b)

Road Junction Superelevation

Procedure

Where a side road junctions on the outside of a small radius curve, a compromise is necessary between adequate superelevation on the through road and safe conditions for vehicles turning against the adverse crossfall. The situation worsens if the curve is located on a steep grade. If the intersection cannot be relocated, the superelevation should be modified to ensure safe turning conditions.

The procedure to be adopted to determine the required superelevation development for a curve is as follows:

Generally, if the side road is important or the curve has a steep longitudinal grade over 5%, the superelevation should not exceed 4% and should preferably be limited to 3%. The same problem does not exist where the junction is on the inside of the curve as the super?elevation then favours the turning movements.

(iii) If calculated value of Gr is less than the values given inTable 2.2.6 (over), the calculated figure should be adopted. If it is greater, the tabulated figure should be used.

2.2.18

(i) Calculate the required length for rotation development (Lr ) [see (c) over]. (ii) Calculate the relative grade G (r ) [see (d) over].

(iv) The selected value of Gr should be substituted in the formula given in e) ( over, to calculate the length of super-elevation development (Le) required to satisfy the relative grade criterion.

Superelevation Development

A profile of a typical superelevation development is shown on Figure 2.2.2.

(v) In most cases the length of superelevation development required for the relative grade criteria L ( e) will be the one adopted, however if the length of rotation development (Lr) exceeds Le then Lr should be selected. Superelevation is applied as shown on Figure 2.2.3.

It can be seen from the diagram that the superelevation development is introduced ahead of the Plan Transition to ensure that a driver does not have to cope with adverse crossfall when beginning to turn.

(c)

60 - 70 percent of the super?elevation development is normally located in advance of the tangent point. This is regardless of the presence of a plan transition. (a)

Satisfactory riding quality is determined by the distance required to uniformly rotate the crossfall from normal to full superelevation.

Length of Superelevation Development

In low speed environments or in mountainous terrain where design speed of the alignment is less than 80km/h, the rate of rotation adopted is 3.5% per second of design travel time.

The desirable length of superelevation development is the length required to uniformly rotate the crossfall from normal to full superelevation with adjustment for the requirements of relative grade.

For design speeds of 80km/h or more the desirable rate of rotation should not exceed 2.5% per second of design travel time.

The length of superelevation development [from near normal crossfall at the S.S. point to near full superelevation at the S.C. point (with allowance made for eases as described below)] should be adequate to give satisfactory riding qualities and to ensure good appearance. The higher the design speed or wider the carriageway the longer the superelevation development.

Length of Rotation Calculation Design Speed