1 Alignment Design Criteria for Dedicated High Speed Railway Lines_Arbind Kumar,Amrendra Jha(RITE

Alignment Design Criteria for Dedicated High Speed Railway Lines Arbind Kumar1 & Amrendra Jha2 Abstract This Paper presents alignment design criteria for the segments of the dedicated high speed railway lines. On these segments, speeds will be above 200 km/h up to a maximum operating speed of 350 km/h and will consider that faster operation up to not less than 400 km/h in future will not be unnecessarily precluded. The Paper defines the geometric design requirements for basic design in order to achieve a safe and reliable operating railway that meets regulatory, operational and performance requirements. The general basis of alignment design will be to follow best practices of the Japanese and European lines and also the guidance of UIC (International Union of Railways) for railway lines, while also taking into account guidance of the Manual for Railway Engineering of the American Railway Engineering and Maintenance of Way Association (AREMA Manual).

1 2

Director (Projects), RITES Ltd., India General Manager (Track & Survey), RITES Ltd., India

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Acronyms AAR AREMA SNCF TSI UIC EU

Association of American Railroads American Railway Engineering and Maintenance of Way Association Société Nationale des Chemins de fer Français (French National Railway Company) Technical Specification for Interoperability of the European Union International Union of Railways European Union

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1.0 Introduction This Paper presents the basis of design and alignment criteria for the segments of the High-Speed Railway (HSR) projects where high-speed trains are operated on tracks dedicated for the purpose. On these exclusive-use segments, speeds will be above 200km/h with an initial maximum operating speed of 300 to 400km/h. Much of what applies to good railway alignment at normal speeds of 100 to 160km/h applies equally well when the design speed is 300km/h, or higher so long as the effects of speed are considered. However, there are a number of “secondary” effects that are minor or unnoticeable at low speeds that do become important as speeds increase. Issues of this nature that affect the alignment will be noted and analyzed in this Paper. 1.1 Statement of Technical Issue The general basis of alignment design, as defined in this document, will follow best practices currently used on the design of HSR systems. Where specific guidance is not provided, the standards described in the Manual for Railway Engineering of the American Railway Engineering and Maintenance of Way Association (AREMA Manual) shall be followed. However, the material presented in the AREMA Manual is defined as “recommended practice” and varies considerably in level of detail and applicability. The UIC (International Union of Railways) has issued, with the cooperation of Japan, Germany and France, documentation from which many technical issues can be derived. More recently, Technical Specifications for Interoperability (TSI) for high-speed railways have been developed by the European Union (EU) to be a set of required standards for all railway systems in the European Union. Codes of practice (EN 13803-1:2010 and EN 13803-2:2006+A1:2009) define track alignment design parameters for plain line and switches and crossings. The alignment shall be developed to afford the highest practical speed that can be attained at a given location in accordance with the basis of design performance requirements concerning operating speed. 2.0 Design Standards and Guidelines 2.1 Basis The general basis for design standards will be the most applicable of the “recommended practice” described in the Manual for Railway Engineering of the American Railway Engineering and Maintenance of Way Association (AREMA Manual). The material presented in the AREMA Manual varies considerably in level of detail and obsolescence. Therefore, a reference to the AREMA Manual without a more specific designation of applicable chapter and section is not sufficient to describe any requirement. Certain UIC documents and the recently developed European TSI and codes provide guidance in areas where the AREMA Manual is either silent or inapplicable. In addition, there have been a number of documents from other sources that are relevant to the alignment design. 2.1.1 The European Union’s (EU’s) Technical Specifications for Interoperability (TSI) The Technical Specifications for Interoperability (TSI) are a set of standards required of all railroad systems in the European Union. For high-speed railway systems, they were first published as Council Directive 96/48/EC - Interoperability of the Trans-European High-Speed Rail System. In the countries that are part of the European Union these standards have the force of law. The TSI are defined and published by subject matter, described as “subsystems”. Requirements of significance to a specific issue may require search of more than a single “subsystem” document, and much of the information is stated in general terms. Each document ends with a country by country description of specific issues relevant to each of the EU countries. The various subsystems are classified as either “structural” or “functional” as follows: Structural Subsystems:  Rolling Stock  Infrastructure  Energy  Control and command and signaling  Traffic operations and management

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Function Subsystems:  Maintenance  Telematics applications for passenger and freight services. The TSI that is primarily relevant to this Paper is that for the Infrastructure Subsystem. Application of the TSI requirements to Indian Projects must be approached with caution, however, as they are based on the historical and current conditions in Western Europe without consideration of practices prevailing in this part of the world. The Infrastructure TSI has limited information relative to alignment. 2.1.2 Other Technical References Recognizing the limitations of the AREMA Manual and the existence of a number of other standards used around the world that have strong experience and theoretical basis in the alignment design of high-speed railroads, the source for some portions of the design requirements can be found in the following other documents:  European Committee for Standardization (CEN standards, specifically EN 13803-1:2010 and EN 13803-2:2006+A1:2009)  UIC Code 703R:1989 – Layout Characteristics of Lines Used by Fast Passenger Trains  UIC – Design of new lines for speeds of 300-350 km/h – State of the Art Report (October 2001)  Engineering studies in support of the development of high-speed track geometry specifications IEEE/ASME joint railroad conference (March 1997)  Taiwan High-Speed Railway Design Manual (2000)  SNCF – High-speed railway design standards (2007 edition) 3.0 Analysis 3.1 Alignment Criteria The alignment of the railroad shall be as smooth as practical with minimal changes in both the horizontal and vertical direction. Appearance, ease of maintenance, and ride quality are all enhanced by a smooth alignment with infrequent and gentle changes in direction. Over 5 changes in direction every 2km shall constitute an Exceptional condition. 3.1.1 Minimum Segment Length due to Attenuation Time All alignment element segments (vertical curves, lengths of grades between vertical curves, horizontal curves, horizontal transitions) shall have a minimum length sufficient to attenuate changes in the motion of the rolling stock. This length is defined by the time elapsed over the segment, and therefore varies directly with design speed. Not all systems have the same time requirements. This attenuation time varies from 1 to 2.4 seconds, and on the SNCF, up to 3.1 seconds at higher speeds. Segment length requirements will govern only where design considerations for the various elements do not require longer segment lengths. Vertical and horizontal alignment sections may overlap. Overlap of horizontal transitions and vertical curves shall be an Exceptional condition. Based on European high-speed rail standards, the minimum distance between the end of a horizontal transition and the beginning of a vertical curve or the end of a vertical curve and the beginning of a horizontal transition is 50m with an Exceptional limit of 30m. Attenuation time, based on the most conservative requirements, shall be:  For V < 300 km/h  Desirable attenuation time: not less than 2.4s  Minimum attenuation time: not less than 1.8s  Exceptional attenuation time: not less than 1.5s  An attenuation time of 1.0s on the diverging route in curves adjacent to or between turnouts  For V>=300 km/h  Desirable attenuation time: not less than 3.1s  Minimum attenuation time: not less than 2.4s  Exceptional attenuation time: not less than 1.8s

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Minimum segment length is calculated by the formula: Lm = (V km/h / 3.6) x tsec Sample minimum segment lengths are presented in Tables 3.1.1 and 3.1.2 below: Table 3.1.1: Minimum Segment Lengths at Various Speeds of 300 km/h and higher Design Speed in km/h 400 355 320 300

Minimum Segment Lengths in m for times of 3.1 sec 2.4 sec 1.8 sec 344 267 200 306 237 178 276 213 160 258 200 150

Table 3.1.2: Minimum Segment Lengths at Various Speeds of up to 300 km/h Design Speed in Minimum Segment Lengths in m for times of km/h 2.4 sec 1.8 sec 1.5 sec 300 200 150 125 280 187 140 117 240 160 120 100 200 133 100 83

1.5 sec 167 148 133 125

1.0 sec 83 78 67 56

Where alignment segments overlap, each change shall be treated as a separate alignment element for the purpose of calculating minimum segment lengths. For example, when there is a vertical curve within the body of a horizontal curve, the parts of the horizontal curve outside of the vertical curve will be treated as separate segments when calculating segment lengths. 3.2 Horizontal Alignment Curve radii will depend upon allowable limits in cant and cant deficiency. Curves should be set to the largest practical radius and have the lowest practical cant and cant deficiency for the following reasons:  Lower cant required to balance equipment speed  Lower cant deficiency  Comfort over a wider range of speeds  Lower wear on rails and forces on equipment In locations where train speeds vary considerably, such as near stations, it is recommended that designers increase curve radii significantly above minimum values. This results in lower levels of cant deficiency, which are less perceptible to riders over ranges of train speed. Alignments consisting of curves that are at or approaching minimum values of radius and maximum or near maximum values of cant and cant deficiency are an indication of a poor quality design. 3.2.1 Cant Design Considerations: The design value of cant will be influenced by:  Maximum Speed Limit  Calculated normal and maximum speeds of high-speed trains, including both through trains and stopping trains.  Allowable limits of actual cant in track  Allowable limits of cant deficiency in track Theoretical Basis: Equilibrium cant can be determined exactly by determining the angle of the plane across the top of rails that would equal the angle from vertical of the vector of centrifugal force and gravity. e=GV2/(127.14xR), where G is the Dynamic Gauge in mm, V in km/h, e in mm

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For standard gauge track (G=1500mm), this formula becomes the familiar formula of: e = 11.8 V2/R (R in m, V in km/h and e in mm) This formula is approximate, but the level of approximation is insignificant. Traditionally, cant has been limited to 6 inches (152 mm) or less in the US and cant deficiency has been limited to 3 inches (76 mm). However, in the past, higher values have been used by some railways in order to allow higher passenger train speeds. Currently, cant limits are commonly set at 4 inches (101 mm) or less in lines that carry high centre of gravity freight and up to 6 inches (152 mm) in lines carrying predominantly passenger traffic. Maximum cant values of 160mm to 180mm are common in passenger carrying lines in Europe. Some systems only allow above 160mm on slab track. On the Shinkansen system, the maximum is 180mm but with up to 200mm under limited circumstances without reference to type of track construction or train speed. 3.2.2 Cant Deficiency Practical limits of cant deficiency are based on passenger comfort. Safe limits for cant deficiency are significantly in excess of comfort limits. The FRA limits Cant Deficiency for US passenger carrying lines to 4 inches (100 mm) and requires a waiver for limits above 3 inches (75 mm). The EU permits higher limits varying between 180mm (for speeds between 80 to 200km/h) and 130mm (at speeds between 250 to 300 km/h). The Shinkansen system allows 110mm without reference to type of track construction or train speed. 3.2.3 Cant Excess There is Cant Excess when the applied cant exceeds the equilibrium value and thus the unbalance is positive. On European railways, the normal limit is 110mm on mixed railways. However, for dedicated HSR, this situation would never really result. It has been noted by many observations in various places that a train traversing a curve at the equilibrium speed tends to “hunt” or otherwise track poorly. Therefore, it is customary on US railways to provide a 25mm cant excess in relation to the normal operating speed (not the design speed) on mixed railways. 3.2.4 Limits for Cant and Cant Deficiency The first of the following tables provide the allowable upper limits for Cant plus Cant Deficiency. Radii developed from these limits determine the smallest Desirable, Minimum, and Exceptional radius that is permissible for any given speed. Table 3.2.1: Maximum Values, Cant plus Cant Deficiency Design Speed km/h =300

Desirable (mm) 150 150

Cant plus Cant Deficiency (mm) Maximum (mm) Exceptional (mm) 230 280 230 250

Table 3.2.2: Maximum Values of Applied Cant Design Speed km/h =300

Desirable (mm) 100 100

Applied Cant (mm) Maximum (mm) 150 150

Exceptional (mm) 180 180

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Table 3.2.3: Maximum Values of Cant Deficiency Design Speed km/h =300

Desirable (mm) 50 50

Cant Deficiency (mm) Maximum (mm) 80 80

Exceptional (mm) 100 80

The Maximum Value of Cant Deficiency is lower than the values permitted by TSI in order to achieve the passenger comfort lateral acceleration threshold value of 0.05g. Note that the Exceptional Cant Deficiency value does not achieve the passenger comfort lateral acceleration threshold value. 3.2.5 Determination of Applied Cant and Cant Deficiency Applied cant shall be set to provide the best practical ride quality to the majority of the passengers on the trains passing over the particular curve without violating limits set by the design criteria. The speed to be used at the design stage of the alignment is the system design speed, not the maximum operating speed limit that is planned to be used at the time of start of operations. At the time of alignment design, the real purpose of determining cant is to determine the length of spiral to be applied to a particular curve. Thus, the highest anticipated speed, cant and cant deficiency shall be used at this stage of the design. However, in the construction of the track, the cant shall be based on the calculated speed on the curve as initially completed. Therefore, the initial cant applied to the track may be less than that used in the calculations for appropriate spiral length. Normal operating practice is based on trains running at slightly less than maximum power and maximum speed so as to provide some allowance to recover lost time. For now, “Normal Speed” shall be considered to be 90% of the calculated maximum speed. The design value of cant will be influenced by:  Maximum Speed Limit  Calculated normal and maximum speeds of high-speed trains in each direction  Where applicable, calculated normal and maximum speeds of high-speed trains slowing for or accelerating from a station stop  Calculated normal and maximum speeds of other passenger trains (where applicable) Design cant shall not exceed the allowable maximum cant. Design cant shall be calculated for each track. It is neither necessary nor in many locations desirable that both main tracks of the line have the same cant on a given curve. Where train speeds differ from the Design Speed, the cant deficiency may be increased up to the Exceptional limit based on the Design Speed, if necessary, to provide a comfortable cant deficiency in relation to the actual train speed. 3.2.6 Curvature Curves should be of a single arc radius. All main track, station track, and yard connection curves shall have transition spirals. Curves of larger than minimum radii require lower amounts of cant, therefore, providing a comfortable ride over a wider range of speeds. Alignments consisting of curves that are all at or approaching minimum values are an indication of a poor quality design. In the cases where there will be significant variability in train speeds, larger radii are preferred to reduce the ride quality issues due to cant and cant deficiency effects that occur with variation between design speed and actual speed of trains on the curve. Curve radii standards provide “Desirable”, “Minimum”, and “Exceptional” values. However, even the desirable figures can be improved upon. A desirable radius is one that is larger than the standard radii, if at all practical, for larger radii are better. Curve radii are determined according to the cant limits given in Section 3.2.4. Tables 3.2.1 and 3.2.2 summarize Desirable, Minimum and Exceptional limits on cant that are used to develop the following minimum radius table, Table 3.2.4. Two values for 300 km/h is a result of the break in allowable cant deficiency in the TSI requirements. Large radius curves (say, R>20,000m) may, however, be avoided from maintenance considerations.

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Table 3.2.4: Minimum Curve Radii Design Speed km/h 400 355 320 300 =(V/3.6)2 / av, where R is in m, V in km/h, Vertical acceleration (av) in m/s2 and the 3.6 factor is necessary for the km/h to m/s conversion.

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European high-speed lines reportedly do not use curves with radius over 40,000m (131,234 feet radius, or a rate of change 0.0762% per 100 feet) due to maintainability concerns. In French practice, it is unnecessary to provide a vertical curve between two gradients when the difference in gradient is less than or equal to 0.1% or 1mm/m, even for design speeds of 350 km/h. Normal practice in Japan and Taiwan is to use Parabolic Vertical Curves. Even though the vertical curves on the Taiwan High-Speed Railway were defined by radius, they were designed and constructed as parabolas, as the preliminary design was by European engineers and the final design and construction was by Taiwanese, Japanese, and American engineers. 3.3.2.3 Comparison between American, European, and Other Vertical Curve Design Practices The difference in elevation between elevations calculated by the two types of curves as laid out is slight, usually under 3 mm at any point on the curve. Differences in maximum vertical curve radius requirements, or in US Customary railroad terminology, minimum rate of change requirements are as follows:  It is reported that European measuring systems and maintenance practices are incapable of measuring vertical curves with radii of over 40,000 m, therefore vertical curves longer than this are prohibited.  Rates of change down to 0.05 percent per 100 feet (Radius = 60,100 m) have been used in the US for many years without any maintainability issues ever being raised.  The AREMA Manual states simply, “Vertical curves should be designed as long as physically and economically possible.”  The Taiwan High-Speed Railway has multiple vertical curves with radii of 100,000m to 300,000m. Conclusion on Length/Radius: No upper limit needs to be set on vertical curve length/radius. Conclusion on type of Vertical Curve: Parabolic vertical curves may be used in order to be in line with common US/Japanese/Taiwanese practice. 3.3.2.4 Vertical Curve Design – Acceleration Rate and Curve Length Vertical curves for passenger trains are set so as to provide a comfortable vertical acceleration rate. Vertical acceleration limits have been set as low as 2.0% of gravity and as high as 6.0% of gravity. The SNCF standards are highest. However there have been complaints of noticeable ride quality issues with these higher values. Since crest vertical curves reduce the vertical component of the train load, high acceleration rates on vertical curves are to be avoided where horizontal curve will have high cant or high cant deficiency. Current AREMA recommendations for vertical curves are for a vertical acceleration of 0.6 ft/s2 for passenger service, which is 1.86% of gravity and a vertical acceleration of 0.1 ft/s2 for freight service, which is 0.31% of gravity. Considering the above, the acceleration values to be used for vertical curves may be as follows:  Desirable: 0.60 ft/sec/sec =0.182 m/s2 (1.86 percent of gravity)  Minimum: 0.90 ft/sec/sec = 0.275 m/s2 (2.80 percent of gravity)  Exceptional: 1.40 ft/sec/sec = 0.427 m/s2 (4.35 percent of gravity) Vertical curve lengths on lines carrying high-speed trains only shall be:  Desirable VC Length: 0.424*V2  Minimum VC Length: 0.281*V2  Exceptional VC Length: 0.181*V2 3.3.3 Vertical Curve / Horizontal Curve Combinations Vertical and horizontal curves can overlap. Crest vertical curves result in a downward acceleration of the vehicle, thereby reducing the gravitational effect. This reduction is small but not insignificant for the vertical curve rates of change.

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3.3.4 Vertical Curves in Spirals Due to potential maintenance difficulties, it is desirable to avoid use of vertical curves in spirals. The desirable distance between end of spiral and beginning of vertical curve or end of vertical curve and beginning of spiral is 50m with a minimum limit of 30m. Overlap between vertical curves and spirals may be permitted as an Exceptional condition, but only where it can be shown that practical alternatives have been exhausted. 4.0 Conclusions The primary objective in setting alignment is to develop the smoothest practical alignment within the limitations imposed by location of stations, urban areas, mountain crossings and major stream crossings as well as environmental and socio-political constraints. It is also important to consider the optimization of earthworks movement, tunnel length, drainage and bridge structures. The radii of horizontal curves, in particular, should be larger than “Desirable” values wherever it is practical to do so. Going below “Desirable” values for various portions of the alignment should not be treated lightly. Very seldom will an alignment as finally designed and built be better than that set out initially. Quite frequently points will be “locked in” very early in the study process. This is particularly true for the horizontal component of alignment. Use of Minimum and Exceptional values should be held back to the greatest extent practicable for use in the adjustments due to unanticipated constraints that will always occur. At frequent intervals, the designer should step back and look at things globally. This, in particular, means plotting condensed profiles, and looking at the layout over long segments. When transitioning from low speed areas to highspeed areas, one may consider the operating characteristics of both presently available trains and characteristics of trains with anticipated improvements in power, acceleration and braking. Sudden jumps in speed do not happen with trains. There should be a relationship between horizontal and vertical alignment standards. For example, there is no point in using vertical curves designed for 350km/h which are adjacent to curves or other constraining elements that permanently restrict speeds to a much lower value. However, the speed used in developing vertical curves should never be lower than that possible under “Exceptional” conditions on adjacent horizontal curves. 5.0 References 1. Manual for Railway Engineering of the American Railway Engineering and Maintenance of Way Association (AREMA Manual) 2. Practical Guide to Railway Engineering, The American Railway Engineering and Maintenance of Way Association 3. Technical Specification for Interoperability, ‘Infrastructure’ Subsystem, EU Directive 96/48/EC as modified by the Commission Decision of 20 December 2007 (2008/217/EC) 4. European Committee for Standardization (CEN standards, specifically EN 13803-1:2010 and EN 13803-2:2006+A1:2009) 5. UIC Code 703R:1989 – Layout Characteristics of Lines Used by Fast Passenger Trains 6. UIC – Design of new lines for speeds of 300-350 km/h – State of the Art Report (October 2001) 7. Engineering studies in support of the development of high-speed track geometry specifications IEEE/ASME joint railroad conference (March 1997) 8. Taiwan High-Speed Railway Design Manual (2000) 9. SNCF – High-Speed Railway Design Standards (2007 edition) 10. Modern Railway Track, 2nd ed., Coenraad Esveld, 2001

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