4 foot 8 inches
Trestles
Buses stop at railroad tracks to make very sure that a train is not coming before they begin to cross the tracks.
The rails themselves are 6 5/8" tall, the top flange is 2 and 22/32" and the bottom flange is 5 and 1/2". Picture a deformed capital 'I'. The weird thing (to me) is the upright portion is only 5/8"...
Standard American Gauge is 4 feet 8 and a half inches.