Passenger Vehicle Braking, Skid Control, and Hazard Response
A loaded bus carries its weight high and stops longer than a car. The exam tests controlled braking, ABS technique, and recovery from skids and off-road excursions.
Stopping distance
Total stopping distance is perception distance, reaction distance, brake lag, and braking distance. At 55 mph you travel about 81 feet per second. Use a one-second gap per 10 feet of vehicle length below 40 mph, and add one second above 40 mph. A 40-foot bus at 55 mph therefore needs a minimum four-second following distance, and more in rain.
Braking technique
With ABS, apply firm steady pressure and hold it; the pedal will pulse, and that is normal. Never pump ABS brakes. Threshold braking is for vehicles without ABS. Brake in a straight line before a curve and use gentle throttle through it. Use the engine retarder so the service brakes are saved for stopping.
Skids and recovery
In a rear-wheel skid, release the brake, steer in the direction you want the front of the vehicle to go, and look where you want to travel. Do not overcorrect. If a wheel drops off the pavement, hold the wheel straight, slow gradually, and return to the lane at low speed after checking traffic.
Worked example
At 55 mph on wet pavement, a driver of a 40-foot bus leaves a three-second gap. That is 243 feet, while wet stopping distance at 55 mph exceeds 300 feet. The gap is too short. Maintain five seconds or reduce speed to roughly 45 mph so the gap covers the stopping distance.
Traps
Braking hard mid-curve; pumping ABS; jerking the wheel when a tire drops off the shoulder; using the retarder on a slick surface where it can start a drive-axle skid.