Air Brake Test Stopping Distance & Brake Performance 1 — Questions and Answers
Question 1: What are the three main components that make up total stopping distance for a vehicle with air brakes?
- Perception distance, reaction distance, and braking distance (Correct answer)
- Brake lag, skid distance, and deceleration distance
- Air pressure buildup, brake application, and wheel lockup
- Driver alertness, road friction, and vehicle weight
Correct answer: Perception distance, reaction distance, and braking distance
Total stopping distance is the sum of perception distance (time to see a hazard), reaction distance (foot moving to brake), and braking distance (vehicle coming to a stop).
Question 2: Approximately how long is the brake lag time for air brakes compared to hydraulic brakes?
- Air brakes lag about 0.4 seconds vs. 0.1 seconds for hydraulic brakes (Correct answer)
- Air brakes lag about 0.1 seconds vs. 0.4 seconds for hydraulic brakes
- Both systems have the same lag time of about 0.2 seconds
- Air brakes lag about 1.0 second vs. 0.5 seconds for hydraulic brakes
Correct answer: Air brakes lag about 0.4 seconds vs. 0.1 seconds for hydraulic brakes
Air brakes have a lag of approximately 0.4 seconds because air must travel through the lines to activate the brakes, while hydraulic brakes respond almost instantly at about 0.1 seconds.
Question 3: At 55 mph on dry pavement, approximately how many feet of additional stopping distance does air brake lag add compared to the moment you press the brake pedal?
- About 32 feet (Correct answer)
- About 10 feet
- About 60 feet
- About 100 feet
Correct answer: About 32 feet
At 55 mph, a vehicle travels roughly 80 feet per second, so 0.4 seconds of brake lag adds approximately 32 feet before braking even begins.
Question 4: A fully loaded truck traveling at 55 mph on dry pavement requires approximately how many feet to come to a complete stop?
- About 335 feet (Correct answer)
- About 150 feet
- About 500 feet
- About 200 feet
Correct answer: About 335 feet
At 55 mph, a fully loaded truck needs roughly 335 feet to stop when accounting for perception, reaction, brake lag, and braking distance on dry pavement.
Question 5: How does vehicle weight affect stopping distance for air-braked vehicles?
- Empty trucks often take longer to stop than fully loaded trucks due to reduced traction (Correct answer)
- Heavier trucks always stop in a shorter distance than lighter trucks
- Vehicle weight has no significant effect on stopping distance
- Loaded trucks always require exactly twice the stopping distance of empty trucks
Correct answer: Empty trucks often take longer to stop than fully loaded trucks due to reduced traction
Empty trucks can require up to 40% more stopping distance than loaded trucks because lighter vehicles have less weight pressing the tires onto the pavement, reducing traction.
Question 6: Which factor has the GREATEST impact on braking distance when descending a steep grade?
- The grade itself increases the speed and force needed to stop, dramatically lengthening stopping distance (Correct answer)
- Downhill grades reduce stopping distance because gravity assists braking
- Only the length of the hill matters, not the steepness of the grade
- Stopping distance on a downgrade is the same as on flat ground if brakes are properly adjusted
Correct answer: The grade itself increases the speed and force needed to stop, dramatically lengthening stopping distance
On a downgrade, gravity continuously accelerates the vehicle while brakes must work against both momentum and gravity, significantly increasing the distance needed to stop.
Question 7: If you double your speed from 20 mph to 40 mph, by approximately how much does your braking distance increase?
- Braking distance increases approximately four times (Correct answer)
- Braking distance doubles
- Braking distance triples
- Braking distance increases by one and a half times
Correct answer: Braking distance increases approximately four times
Braking distance increases with the square of speed; doubling speed from 20 to 40 mph quadruples the braking distance because kinetic energy is proportional to velocity squared.
Air Brake Test Stopping Distance & Brake Performance 1
What are the three main components that make up total stopping distance for a vehicle with air brakes?