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Maximum Allowable Speed on Curve

[+] Author Affiliations
Nazmul Hasan

SNC-Lavalin Inc., Vancouver, BC, Canada

Paper No. JRC2011-56007, pp. 1-9; 9 pages
  • 2011 Joint Rail Conference
  • 2011 Joint Rail Conference
  • Pueblo, Colorado, USA, March 16–18, 2011
  • ISBN: 978-0-7918-5459-4 | eISBN: 978-0-7918-3893-8
  • Copyright © 2011 by ASME


It is generally recognized by FRA, AREMA, Amtrak, OSHA, and many other applicable authorities that the maximum acceptable rate of radial acceleration for passengers comfort is 0.1g, where ‘g’ is 9.81 m/s/s. Jerk is limited to 0.03g/s. In the industry the maximum allowable speed (km/h) is calculated by:

Vmax = (Ea + Eu)R11.8
where Eu′ = Blanket unbalance usually greater than design unbalance (mm); Ea = Actual superelevation applied to track (mm); R = Curve radius (m). Clearly the purpose of the equation is to achieve a gain in speed with using the existing spiral at the cost of the comfort limit. It appears that there is a consensus in breaking the standard comfort limit. The value of blanket unbalance varies from operator to operator e.g. 65mm, 75mm, 100mm etc. This variation indicates that there is no consensus in an upper limit beyond standard passenger comfort limit to determine the maximum allowable speed. This is the main reason behind the variation of unbalance, Eu′ adopted by different railways. Other minor reasons are ability of the vehicle to negotiate unbalance, strength of track to withstand lateral load, maintenance standard of track etc. Current use of blanket unbalance superelevation for all types of curves is flawed because it leads to different values of jerk depending on design speed, radius, and incremental unbalance on top of design unbalance. Among these different values of jerk, all values may not be acceptable. The current practice of using a blanket unbalance superelevation may not generate the maximum allowable speed. Intuitively the actual and unbalance superelevation should vary together such that a higher unbalance should go with higher actual superelevation to ensure a consistent comfort. Thus the unbalance should be different for each individual curve. To overcome the weaknesses of using a blanket unbalance superelevation and to gain higher speed, a new formula is suggested.

Copyright © 2011 by ASME



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