First, it must be able to exert a tractive force sufficient to start the train under the worst conditions possible on the railway over which it is to operate - for instance, when the train is stopped by signal on a rising gradient where the track is curved and fitted with a guard-rail.
an hour and a guard-rail insisted on inside the curve.
There should be an adequate handhold at all times or, where there is no handhold a guard rail must be used.
plumb line or a long straight edge, or the guard rail of an elevated platform, to get a level top.
Current regulations state that there should be less than 3.5 inches between the guard rail and the mattress.