Why should you never use the trailer's spring parking brakes as a substitute for the service brakes while the vehicle is moving?

Pick an answer

1. It only wastes air pressure and has no effect on trailer handling
2. Applying them at speed can cause the trailer wheels to lock and the trailer to skid, since they are not designed for graduated braking
3. It is illegal but not actually dangerous
4. It has no real risk, since spring brakes are just as smooth as service brakes at speed and never lock the wheels

Correct!

Not quite. The correct answer is highlighted.