Air Brake Test Stopping Distance & Brake Performance 2 — Questions and Answers
Question 1: How does wet pavement affect the stopping distance of a vehicle with air brakes?
- Wet pavement can double the stopping distance compared to dry pavement (Correct answer)
- Wet pavement reduces stopping distance by 10 percent
- Wet pavement only affects stopping distance at speeds above 65 mph
- Wet pavement has no effect on air brake stopping distance
Correct answer: Wet pavement can double the stopping distance compared to dry pavement
Wet pavement significantly reduces tire-to-road friction, which can approximately double the stopping distance compared to dry conditions.
Question 2: What happens to stopping distance when wheel brakes are out of adjustment on a multi-axle vehicle?
- Stopping distance increases because fewer brakes are doing the work (Correct answer)
- Stopping distance is unaffected because the remaining brakes compensate automatically
- Stopping distance decreases because the vehicle is lighter without working brakes
- Out-of-adjustment brakes lock up sooner, reducing stopping distance
Correct answer: Stopping distance increases because fewer brakes are doing the work
When brakes are out of adjustment, those brake assemblies contribute less stopping force, meaning fewer brakes must do all the work, significantly increasing stopping distance.
Question 3: Which condition is MOST likely to cause brake fade on a long downhill grade?
- Continuous heavy braking that overheats the brake drums and linings (Correct answer)
- Using the service brakes in short controlled applications
- Engaging the engine brake at the top of the grade
- Checking air pressure before beginning the descent
Correct answer: Continuous heavy braking that overheats the brake drums and linings
Continuous heavy braking generates heat that raises drum and lining temperatures until the friction material can no longer effectively slow the vehicle, causing brake fade.
Question 4: What is the recommended technique to avoid brake fade on a long, steep downgrade?
- Select a low gear before starting down and use light steady brake applications to control speed (Correct answer)
- Pump the brakes rapidly at regular intervals throughout the descent
- Apply maximum brake pressure continuously at the start and then release
- Rely entirely on the service brakes and avoid using the engine retarder
Correct answer: Select a low gear before starting down and use light steady brake applications to control speed
Using a low gear to harness engine braking combined with light, steady service brake applications controls speed without overheating the brakes.
Question 5: How does a properly adjusted automatic slack adjuster contribute to optimal stopping distance?
- It maintains the correct pushrod stroke length so brake shoes contact the drum with full force (Correct answer)
- It reduces air pressure requirements so the compressor cycles less frequently
- It eliminates brake lag entirely by pre-loading the brake chambers
- It prevents wheel lockup by automatically modulating air pressure
Correct answer: It maintains the correct pushrod stroke length so brake shoes contact the drum with full force
Proper slack adjuster adjustment ensures the brake lining contacts the drum at the correct distance, delivering maximum braking force with each application.
Question 6: At 60 mph, approximately how far does a truck travel during the driver's perception and reaction time before the brakes are even applied?
- About 132 feet (Correct answer)
- About 50 feet
- About 200 feet
- About 75 feet
Correct answer: About 132 feet
At 60 mph, a vehicle travels roughly 88 feet per second, and with a 1.5-second combined perception-reaction time, the truck covers approximately 132 feet before braking begins.
Question 7: Which of the following road conditions causes the GREATEST reduction in tire-road friction and the longest stopping distance?
- Black ice on pavement (Correct answer)
- Wet pavement during rain
- Packed gravel road
- Dry concrete road surface
Correct answer: Black ice on pavement
Black ice is nearly frictionless and can increase stopping distance by ten times or more compared to dry pavement, making it the most dangerous surface condition.
Air Brake Test Stopping Distance & Brake Performance 2
How does wet pavement affect the stopping distance of a vehicle with air brakes?