Vehicle Controls, Braking Systems, and Antilock Brakes on Buses
Controls and braking hardware
Know the function of the parking brake (spring-applied, air-released on air-brake buses), the service brake, the retarder, and the engine brake. Retarders and engine brakes assist on downgrades but do not replace the service brake, and they should be switched off on slippery surfaces because they can cause drive-wheel skids. The parking brake must hold the bus on a grade.
Air brakes
Air-brake buses have a dual-circuit system with a low-air warning that must activate before pressure falls below a set threshold, and spring brakes that apply automatically when pressure drops too low. Know the buildup test and the leak-down limits. A bus that loses air pressure will stop on its own once pressure falls far enough - but you should act before that, pulling off safely.
Antilock brakes
ABS prevents wheel lockup during hard braking and helps retain steering control. It does not shorten stopping distance on all surfaces, and it does not replace safe following distance. When ABS activates, hold firm, steady pressure and steer - do not pump the brake. The ABS lamp should come on at start and go out; if it stays on, the system has a fault and you should report it, though normal braking remains.
Traps
Questions like to claim ABS lets you brake later or that pumping the pedal helps. Others confuse the parking brake type or suggest using a retarder on ice. Remember that the low-air warning is checked before the bus is driven, not after.
Rule of thumb
Firm, continuous pedal pressure with ABS; steer around the hazard rather than pumping.