4 ms·

Speed limits are set for passenger comfort rather than the fastest speed a train could safely travel. The equation for the speed limit for a curve is a combina

Speed limits are set for passenger comfort rather than the fastest speed a train could safely travel. The equation for the speed limit for a curve is a combination of the radius of the curve, the relative elevation of the outside rail (superelevation) and the allowable “unbalanced superelevation” of the train itself, how much lateral force the train is permitted to have going around the curve. You could design a railroad where the outside rail was raised enough to not feel any lateral forces effects of curves, but speeds will be much lower. Typical trains have 3 or 4 inches of unbalanced superelevation, but a tilting train can drive this number much higher to 7 to 9 inches. This allows faster speeds and maintains passenger comfort.

iggldiggl 6y ago
3 or 4 inches seems a tad on the low side, but then again I remember somebody giving an example of a US tilting train being barely faster than a conventional European train on a similar curve due to more conservative standards prevailing across the pond. In Germany, up to ~5" (130 mm) are permissible on the main line network. In theory and exceptionally, even values up to 6" (150 mm) are possible, although haven't really been used in practice so far as far as I know. The maximum speed for trams/streetcars/light rail is often based on a maximum deficiency of 150 mm, too. Tilting trains in Germany can use up to ~12" (300 mm) of cant deficiency, but then again in Germany they really seem a dead end so far.