Speed & Space Management

Study questions with answers

12 sample Speed & Space Management questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. Why should you not fully trust the posted clearance height at a bridge or overpass?

   Correct answer: Repaving or a tall load can make the real clearance less than posted

   Repaving or packed snow can reduce the real clearance below the posted number, and a load can make your vehicle taller. If you are not sure your vehicle will fit, slow down and find another route.

   Source: California CDL Manual — Section 2: Driving Safely (Managing Space)

2. 2. Total stopping distance for a commercial vehicle is made up of which three parts?

   Correct answer: Perception distance, reaction distance, and braking distance

   Total stopping distance equals perception distance plus reaction distance plus braking distance. All three add up to the space you need before the vehicle can come to a full stop.

   Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)

3. 3. About how far does a heavy vehicle travel before stopping from 55 mph on a dry road?

   Correct answer: About 400 feet — longer than a football field

   Adding perception, reaction, and braking distance, a truck needs roughly 400 feet to stop from 55 mph — longer than a football field. This is far greater than most drivers expect, so keep plenty of space ahead.

   Source: California Commercial Driver Handbook — Driving Safely (Controlling Your Speed)

4. 4. Compared with a loaded truck, how does an empty truck usually stop?

   Correct answer: It can take a longer distance to stop because of less traction

   An empty truck often needs a LONGER distance to stop, because it has less traction. With less weight pressing the tires down, the wheels lock up more easily and the vehicle can skid.

   Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)

5. 5. At speeds below 40 mph, what is the recommended following distance for a commercial vehicle?

   Correct answer: One second for each 10 feet of vehicle length

   Allow one second of following distance for each 10 feet of vehicle length at speeds under 40 mph. For example, a 40-foot vehicle should keep at least a 4-second gap.

   Source: California CDL Manual — Section 2: Driving Safely (Managing Space)

6. 6. What is the purpose of a runaway-vehicle escape ramp on a steep downgrade?

   Correct answer: To safely stop a vehicle whose brakes have failed

   An escape ramp is built to stop a runaway vehicle safely, usually with soft gravel or sand and an uphill slope. If your brakes fail on a downgrade, using the ramp can prevent a deadly crash.

   Source: California Commercial Driver Handbook — Driving Safely (Mountain Driving)

7. 7. How should you adjust your speed on wet roads?

   Correct answer: Slow down, because stopping distance increases on wet roads

   Slow down on wet roads, because they reduce traction and can roughly double your stopping distance. Reduce speed by about a third on wet pavement and more on snow or ice.

   Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)

8. 8. On a long downgrade, what should be your main way of controlling speed?

   Correct answer: The braking effect of the engine in a low gear

   The engine's braking effect in a low gear is your primary way to control speed on a downgrade. Use the brakes only to supplement the engine, so they do not overheat and fade.

   Source: California CDL Manual — Section 2: Driving Safely (Controlling Your Speed)

9. 9. Because a loaded commercial vehicle accelerates slowly, what do you need before crossing or pulling into traffic?

   Correct answer: A much larger gap, because you accelerate slowly

   You need a much larger gap than a car would, because your heavy vehicle takes far longer to get up to speed. Make sure there is plenty of room before you pull out.

   Source: California CDL Manual — Section 2: Driving Safely (Managing Space)

10. 10. What causes brakes to "fade" and lose stopping power on a long downgrade?

    Correct answer: Overheating from using the service brakes too much

    Using the service brakes too much on a long grade overheats them, and overheated brakes lose their ability to slow the vehicle. To prevent fade, pick a safe speed and use the engine's braking effect in a low gear.

    Source: California Commercial Driver Handbook — Driving Safely (Controlling Your Speed)

11. 11. Why should you avoid driving right alongside another vehicle on a multi-lane road?

    Correct answer: You may be in a blind spot and have no room to escape a hazard

    Traveling beside another vehicle puts you in its blind spot and leaves you no room to steer aside if you must avoid a hazard. It is safer to drop back or move ahead so you keep open space around you.

    Source: California Commercial Driver Handbook — Driving Safely (Managing Space)

12. 12. If you double your speed, about how much does your braking distance change?

    Correct answer: It becomes about four times as long

    Braking distance grows with the square of speed, so doubling your speed makes the braking distance about four times as long. That is why small increases in speed greatly increase how far you need to stop.

    Source: California Commercial Driver Handbook — Driving Safely (Controlling Your Speed)