A spring brake is held in the released position while you drive. What actually holds it off?
- The driver keeping the parking control pushed in
- Air pressure pushing against a strong spring
- A mechanical latch that the spring locks into
- The rotation of the wheel, which pulls the shoe clear
The answer is B
A spring brake contains a powerful spring that is trying to apply the brake all the time, and air pressure is the only thing holding that spring compressed. Driving is therefore the state that has to be maintained, and braking is what the unit falls back to on its own. That single point explains almost everything else the system does.
Motor Vehicle Act (British Columbia)


