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. If you double your speed, about how much does your stopping distance increase?

   Correct answer: About four times as much

   Doubling your speed roughly quadruples the distance needed to stop and multiplies the crash energy about fourfold.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (The Effect of Speed on Stopping Distance)

2. 2. Why should you not rely only on posted clearance heights at bridges and overpasses?

   Correct answer: Repaving or packed snow may have lowered the actual clearance

   Repaving or packed snow may have reduced the clearance since the height was posted, and an empty van is taller than a loaded one.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Space Overhead)

3. 3. What should be your principal method of controlling speed on a long, steep downgrade?

   Correct answer: The braking effect of the engine

   Let engine braking be your primary means of holding speed down a grade, keeping the service brakes in reserve for when you actually need to slow or stop.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Speed on Downgrades)

4. 4. Why does an empty truck often require a greater stopping distance than a loaded one?

   Correct answer: An empty vehicle has less traction and can lock its wheels

   With less traction, an empty truck tends to bounce and its wheels can lock, so braking is far worse than when the vehicle is loaded.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (The Effect of Vehicle Weight on Stopping Distance)

5. 5. About how much can a wet road increase your stopping distance?

   Correct answer: It can double the stopping distance

   A wet surface can double your stopping distance, so reduce speed enough to halt within the distance a dry road would allow.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Matching Speed to the Road Surface)

6. 6. At speeds below 40 mph, how much following distance should you keep for the length of your vehicle?

   Correct answer: One second of space for every 10 feet of your vehicle's length

   Below 40 mph, allow at least one second of following distance for each 10 feet of vehicle length.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (How Much Space?)

7. 7. What can happen if a truck with a high center of gravity takes a curve too fast?

   Correct answer: It can roll over even at the posted curve speed

   Testing has demonstrated that a high center of gravity can flip a truck even at a curve's posted limit, so reduce to a safe speed before you enter.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Speed and Curves)

8. 8. In roadway work zones, what is the leading cause of injuries and fatalities?

   Correct answer: Speeding traffic

   Traffic moving too fast is the top killer and source of injury in work zones, so always obey the posted limits there.

   Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Roadway Work Zones)

9. 9. Compared with hydraulic brakes, what extra factor adds to the stopping distance of an air-brake vehicle?

   Correct answer: Brake lag, the delay before the brakes take hold

   Air brakes add 'brake lag' — the time for air to flow through the lines — which adds about 32 feet at 55 mph before the brakes take hold.

   Source: Pennsylvania CDL Manual — Section 5: Air Brakes (Stopping Distance)

10. 10. When traveling faster than 40 mph, how do you adjust your following distance?

    Correct answer: Add one second for safety

    At speeds above 40 mph you must add one second to the following distance you would use at lower speeds.

    Source: Pennsylvania CDL Manual — Section 2: Driving Safely (How Much Space?)

11. 11. When should you shift into a low gear for a downgrade?

    Correct answer: Before you start down the grade

    Select a low gear before you begin the descent; trying to downshift once your speed has climbed may leave you unable to get into any gear at all.

    Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Select the Right Gear Before Starting Down the Grade)

12. 12. At what speed can hydroplaning occur when there is a lot of water on the road?

    Correct answer: As low as 30 mph

    When water is heavy on the road, a vehicle can begin to hydroplane at speeds down around 30 mph, and low tire pressure or worn tread makes it more likely.

    Source: Pennsylvania CDL Manual — Section 2: Driving Safely (Identifying Slippery Surfaces)