Click for next page ( 44


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 43
43 4.9 Infrastructure Guidelines as to hold the track against lateral movement. Heavier grade ballast will help maintain track alignment. 4.9.1 Application One of three situations will apply as shown in Table 4-8. 4.9.4 Wheel-Rail Interface Guidelines The third situation is quite common on older European sys- tems where, although LFLRVs have been introduced, LFLRVs The wheel-rail interface must be compatible in all situa- are often confined to certain routes until other routes are tions. The wheel and rail profile should be such that there is modified. The split in the level of detail in the specification contact over the designed contact area on the wheel tread and between the transit system and the infrastructure supplier, in the wheel flange. At the same time, contact bands must not be Situations 2 and 3, will vary in a similar way to that for vehi- too wide because such bands might be a cause of rolling con- cle specifications as discussed in Section 4.4. The fundamen- tact fatigue (see Section 3.6.2). tal Guidelines 2 and 3 (see Section 4.3) apply to infrastructure and are essential to ensure trouble-free performance. Infra- 4.9.5 Switches and Crossings structure standards will apply in all the scenarios described in Table 4-1. One of the main objectives of specifying features of switches and crossings when LFLRVs are operated is to minimize derailment risks associated with IRWs on the 4.9.2 Track Geometry Standards types of center truck used. This can be achieved by a Table 4-9 shows the track geometry guidelines suggested smooth passage and reducing the freedom for wheels to for existing and new systems using LFLRVs. It is very impor- take a wrong path. tant to get the gauge and position of restraining rail correct The following guidance is based on the research findings on curves. and an earlier TCRP report (1). In this case we need to recon- sider Table 4-1. In Situations A, C, and D, the switches and crossings will already exist and they may or may not be suit- 4.9.3 Track Guidelines able. As a minimum, they should be modified so as to allow New systems should consider using 115 RE rail. For LFLRVs to operate safely. It is difficult to generalize what will embedded track, the matching rail is either Ri59/13 or be required to do this because of the possible variations in Ri59N grooved rail or 115 RE with a formed groove along- track geometry and vehicle, but one might side. 115 RE rail should be inclined at 1 in 40--this will match the profile of RI59 where the latter is laid without any Change the type of switch, inclination. In some cases, these sections will not be appro- Change the "number" of the switch to give a less acute priate, but care needs to be taken to select a rail section that switch angle, matches these sufficiently well so that wheel profiles can be Provide more guard rails, modified if necessary. Improve the embedding of the switchblades into the run- Older systems should replace their rail with these sections ning rails, and/or when rail becomes due for renewal and should replace it Provide cover guards (house tops). when introducing LFLRVs if the business case makes sense. Otherwise they should continue with the rail sections in use. Table 4-10 shows guidance for switches and crossings in The track base must remain as level and twist free as possi- Situations B and E. In Situation B it is still difficult to gener- ble so the specifications for new lines should include features alize in all areas because of variations in vehicle parameters. to make the track maintain its alignment. Older track should In Situation E, however, one can assume that the vehicles and be upgraded to this guideline or operated at reduced speed. track will conform to the guidance given so far in these guid- Where ballast is used, ballast shoulders should be created so ance notes. Table 4-8. Situations where infrastructure standards will apply. Situation Description Who sets and applies the standards 1 An existing system that is introducing LFLRVs. Transit system 2 A new system that will use LFLRVs. Transit system/infrastructure supplier 3 An existing system that will have new Transit system/infrastructure supplier extensions that will use LFLRVs but where the standards need to allow for compatibility with existing routes.

OCR for page 43
44 Table 4-9. Suggested track geometry guidelines. Feature Existing systems New systems Note Nominal track gauge As existing unless a business 56.5 inches/1435 Use of standard gauge case can be made for mm (or close gives maximum choice conversion to 56.5 inches equivalent). of supplier. (1,435 mm.) Tangent track gauge As existing but modify if Based on nominal See Section 3.6.5. appropriate. track gauge, wheel profile, and new build tolerances. Minimum curve radius As existing but try to avoid 82 feet (25 m). For each curve use as regular use of unusually large a radius as sharp curves if possible. practical, especially on frequently used track. Gauge widening on As existing but modify if None. See Section 3.6.5. tight radius curves appropriate. Minimum tangent track As existing but modify if Length = 0.35V Transition curves should between curves appropriate. where V = be used wherever operating speed possible. (mph), or 66 yards, whichever is greater. Vertical curvature As existing. Appropriate for Combinations of sharp vehicle geometry. horizontal and vertical curves are to be avoided. Rail inclination As existing. Depends on rail type. Flangeway clearance As existing. Minimum 0.2 See Section 3.6.5. inches (5 mm), ideally 0.28-0.31 inches (7-9 mm) Where should Conform to existing practice. Apply U.S. restraining rail be Standard. provided? Flangeway width Existing. 111/16 inch (42 mm) Flangeway dimensions preferred unless correspond to those of unsuitable. RI59 rail. Flangeway depth Existing. 17/8 inch (47 mm) preferred unless unsuitable. Table 4-10. Guidance on switches and crossings. Feature Situation B (Existing vehicles) Situation E (New vehicles) Type of switch Flexible switch rails rather than pivoting switchblades; swing nose frogs operation are ideal. Stock rail contact Make use of undercut blades (e.g. Samson switches) Embedment Make use of elastomer to reduce noise Guard rails Adjustable so that they can be set accurately. Switch rail tip Adapt to suit vehicles Design to avoid flange angle issues design Fully guarded Provide if necessary at vulnerable Avoid need by good overall system switches locations design House tops Provide if necessary at vulnerable Avoid need by good overall system locations design Flangeway As constant as possible, acting like the plain line situation. Flangeway Minimum 11/2 inches (38 mm) wide. 13/8 - 11/2 inches clearances (35-38 mm) deep (U.S. Standard) Minimum size As existing but improve if #10. #8 in crossovers, #6 in yards. possible.