The Dimensions of Railroad Tracks
A primary role of the Federal Railroad Association (FRA) is to tactically inspect track conditions to decide whether a railroad is obeying with federal safety standards. One of the main aspects they check is in the area of track geometry. This includes its gauge, alignment, elevation, curvature, and track surface. A track's gauge is the distance between the rails. The alignment is the straightness of the tracks, each rail, or the track centerline. The elevation is height above ground level. The curvature is the quantity by which the rail strays from straightness. The track surface is the smoothness or flatness of the track. In order to check these, a track geometry car is used. It is an automated inspection vehicle that examines numerous geometric parameters of the track without getting in the way of usual railroad procedures. The FRA has three of these cars, which run throughout the country as part of the Automated Track Inspection Program.
Below are a few charts that indicate the standard dimensions of railroad tracks as well as other components of the railway (Source: http://urbaneagle.com/data/RRstddims.html):
