No person may drive any of the following vehicles on a highway at a speed in excess of 55 miles per hour:
- (a) A motortruck or truck tractor having three or more axles or any motortruck or truck tractor drawing any other vehicle.
- (b) A passenger vehicle or bus drawing any other vehicle.
- (c) A schoolbus transporting any school pupil.
- (d) A farm labor vehicle when transporting passengers.
- (e) A vehicle transporting explosives.
- (f) A trailer bus, as defined in Section 636.