Passenger buses and motor homes longer than thirty-five feet, but not longer than forty-five feet, may be operated on the streets of cities and towns when authorized pursuant to § 46.2-1300. Passenger buses and motor homes may exceed the forty-five-foot limitation when such excess length is caused by the projection of a front or rear safety bumper or both. Such safety bumper shall not cause the length of the bus to exceed the maximum legal limit by more than one foot in the front and one foot in the rear. “Safety bumper” means any device which may be fitted on an existing bumper or which replaces the bumper and is so constructed, treated, or manufactured to absorb energy upon impact.