Final answer:
Vehicles must not park within 50 feet of railroad tracks when stopping at a railroad grade crossing.
Step-by-step explanation:
According to the Department of Transportation's Federal Motor Carrier Safety Administration, vehicles must not park within 50 feet of railroad tracks when stopping at a railroad grade crossing, unless otherwise indicated by signs or signals. This distance is necessary to ensure that vehicles and pedestrians have enough space to safely maneuver around trains and avoid potential accidents and collisions.