49 C.F.R. § 213.53 : Transportation — OTHER REGULATIONS RELATING TO TRANSPORTATION — FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION — TRACK SAFETY STANDARDS — TRACK GEOMETRY — Gage

(a) Gage is measured between the heads of the rails at right-angles to the rails in a plane five-eighths of an inch below the top of the rail head.

(b) Gage shall be within the limits prescribed in the following table-

Class of track	The gage must be at least-	But not more than-
Excepted track	N/A	4'10 1/4 inch.
Class 1 track	4'8 inch	4'10 inch.
Class 2 and 3 track	4'8 inch	4'9 3/4 inch.
Class 4 and 5 track	4'8 inch	4'9 1/2 inch.

49 C.F.R. §213.53