For what it's worth , the FRA Code of Federal Regulations uses the spelling of "gage" in all regulations pertaining to track geometry and track safety standards. Example below:
§213.53 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′101⁄4 ″. |
| Class 1 track | 4′8″ | 4′10″. |
| Class 2 and 3 track | 4′8″ | 4′93⁄4 ″. |
| Class 4 and 5 track | 4′8″ | 4′91⁄2 ″. |
