Vehicle Controls, Braking, and Handling
Vehicle Controls, Braking, and Handling
This domain tests control of a large passenger vehicle, especially air brakes, stopping distance, and the geometry of turns. The exam rewards smooth, planned driving over reactive correction.
Core rules
- Know the air brake system: pressure buildup, low-pressure warning, spring brakes, and the parking brake. Do not drive with a low-pressure warning.
- Use the brake-door interlock as a check: the bus should not move with the door open if the interlock is working. Never rely on it instead of setting the parking brake.
- Brake early and smoothly. Passenger buses need longer stopping distances when loaded; passengers may be standing.
- On downgrades, select a lower gear before the grade and use engine braking or a retarder to control speed. Do not ride the service brakes.
- Account for tail swing: the rear of the bus swings opposite the turn. Check mirrors and allow clearance.
- Account for off-tracking: the rear wheels follow a tighter path than the front wheels. Swing wide before a turn without crossing into oncoming traffic.
- Adjust speed for rain, ice, and curves. Avoid sudden steering and hard braking that can cause a skid or throw standing passengers.
Worked example
A loaded bus approaches a long downgrade. The driver shifts to a lower gear, sets a safe speed at the top, and uses the retarder plus light brake applications. If the service brakes are used continuously, they can overheat and fade, leaving the bus without adequate stopping power. The correct plan is speed control before the grade, not braking midway down.
Traps
Using the retarder as the primary brake on a slippery surface. Fanning air brakes until pressure drops. Forgetting tail swing when pulling away from a curb. Turning too sharply and letting the rear wheels off-track over a curb. Assuming a light bus stops like a loaded one.