I disagree with the approach to the cant constant as detailed above. Using 11.82 for all the UK tracks is an easy solution to an issue, which doesn't need to be. 11.82 is only correct for CEN56 S&C with 1432mm gauge and 70mm rail head. When NR60 plainline is considered (1438mm gauge and 72mm rail head) the constant changes to 11.88. The difference appears to be small but I had the issue of exceeding 100% deficiency/cant ratio in 2010 when I was working on Alexandra Palace track design. The design had been produced by another designer not to exceed the above ratio with the pway maths sheet having 11.82 embedded into the formula to calculate the equilibrium cant. Because of the speed, proposed curve radius and applied cant, the ratio was exactly 100%. However, when the cant constant was corrected for the track gauge and type in the formula, the ratio exceed 100%, which had to be justified as a variation whereas the curve radius could have been slightly modified to avoid this exceedance had the correct constant been used. Admittedly such scenarios do not happen very often. Now with the introduction of NR60 MKII S&C suit, which uses 1435mm gauge and 72mm rail head dimension, CEN56 S&Cs will be used less often. Maybe now is the time to start updating things that were inherited. The calculations for the cant constant are straight forward and adding it into the software will require additional parameter box to be inputted by the user; the rail gauge (or for the UK practices 11.86 for 1435mm gauge and 11.88 for 1438mm gauge could be added to the code although I would like to see the same functionality as in BRT).
↧