On a combination vehicle, does applying the parking brake apply it to the tractor only, or to the trailer as well?

Pick an answer

1. Parking brakes do not exist on combination vehicles at all
2. It depends on the vehicle's setup, but on many combinations the parking brake control applies spring brakes on both the tractor and trailer together
3. The parking brake can only ever apply to the tractor, never to a trailer's own brakes, since trailers rely only on the service brakes
4. The parking brake applies only to the trailer and has no effect on the tractor at all

Correct!

Not quite. The correct answer is highlighted.