Air Brake Test Air Brake Driving Techniques & Vehicle Control 2 — Questions and Answers
Question 1: What is the recommended following distance for a truck with air brakes at highway speeds?
- One second for every 10 feet of vehicle length (Correct answer)
- At least 4 seconds regardless of vehicle size
- One car length per 10 mph of travel speed
- Two seconds minimum at any speed
Correct answer: One second for every 10 feet of vehicle length
The CDL standard is one second per 10 feet of vehicle length, plus extra time at speeds over 40 mph.
Question 2: What is 'air brake lag time'?
- The time for air pressure to build from zero after starting the engine
- The delay between pressing the brake pedal and the brakes actually applying force (Correct answer)
- The time needed to drain all air tanks after parking the vehicle
- The delay before the low-pressure warning light activates in the cab
Correct answer: The delay between pressing the brake pedal and the brakes actually applying force
Air brake lag is typically about one-half second, during which the vehicle continues moving at full speed before braking begins.
Question 3: Which three components combine to make up the total stopping distance for a truck with air brakes?
- Tire wear distance + brake lag distance + vehicle length
- Perception/reaction distance + brake lag distance + actual braking distance (Correct answer)
- Braking distance + vehicle length + following distance
- Air build-up time + reaction distance + skid distance
Correct answer: Perception/reaction distance + brake lag distance + actual braking distance
Total stopping distance is the sum of how far the truck travels during perception/reaction, during brake lag, and during actual braking.
Question 4: At 55 mph on dry pavement, approximately how many feet does a fully loaded large truck typically need to stop?
- About 100 feet
- About 170 feet
- About 230 feet
- About 300 feet or more (Correct answer)
Correct answer: About 300 feet or more
A fully loaded truck at 55 mph on dry pavement can require 300 feet or more to stop safely when all factors are included.
Question 5: Why can a fully loaded truck sometimes require more stopping distance than an empty truck?
- Loaded trucks always stop faster because the extra weight improves tire contact
- Greater mass means more kinetic energy must be dissipated during braking (Correct answer)
- Air brakes are mechanically less effective when carrying heavy loads
- Loaded trucks require lower air pressure, which reduces braking force
Correct answer: Greater mass means more kinetic energy must be dissipated during braking
Greater vehicle mass means significantly more kinetic energy at the same speed, requiring more braking force and distance to stop.
Question 6: How does wet or icy pavement affect the stopping distance of a truck with air brakes?
- It decreases stopping distance because water cools the brakes
- It remains the same if the driver applies the brakes correctly
- It increases significantly due to reduced friction between tires and road (Correct answer)
- It increases only slightly if the tires are in good condition
Correct answer: It increases significantly due to reduced friction between tires and road
Reduced tire-road friction on wet or icy surfaces greatly increases stopping distance regardless of braking technique.
Air Brake Test Air Brake Driving Techniques & Vehicle Control 2
What is the recommended following distance for a truck with air brakes at highway speeds?