Speed over a particular track segment is governed by (among other things such as curvature, civil speed limits and signaling systems), the FRA track class. Class 4 track, for exammple allows 60 mph freight, 80 mph passenger. Class 4 track must remain below 57' 1/4" gage with no more than 1 1/2 inch vertical deviation within 62 feet. Railroads may set lower speeds for whatever reason but maintain the track to that standard.