No vehicle shall be permitted in, at or upon any terminal or terminal highway unless it shall be in sound mechanical order, shall have adequate lights, horn and brakes and clear vision from the driver's seat. Trailers and semitrailers shall not be permitted unless they are equipped with reflector buttons and unless they shall be equipped with proper brakes so that when disengaged from a towing vehicle, neither aircraft propeller blast nor wind shall cause them to become free rolling. Positive locking couplings shall be required for all towed equipment.