PennDOT Commercial Driver's License 3 — Questions and Answers
Question 1: When backing a tractor-trailer, a driver should primarily use which mirrors?
- Only the right-side mirror
- Both side mirrors and get out to check when uncertain (Correct answer)
- Only the left-side mirror
- The rear-view mirror inside the cab
Correct answer: Both side mirrors and get out to check when uncertain
Drivers should use both side mirrors and physically check the area (get out and look) when uncertain to ensure safety while backing.
Question 2: What is the maximum allowable blood alcohol content (BAC) for CDL holders operating a commercial motor vehicle?
- 0.08%
- 0.04% (Correct answer)
- 0.06%
- 0.02%
Correct answer: 0.04%
The legal BAC limit for CDL drivers operating a CMV is 0.04%, half the standard limit for non-commercial drivers.
Question 3: Which of the following describes a 'runaway truck ramp' and when it should be used?
- A designated area for overnight parking on steep grades
- An escape ramp used when brakes fail on a downgrade (Correct answer)
- A weigh station bypass for trucks under the weight limit
- A lane reserved for trucks traveling uphill
Correct answer: An escape ramp used when brakes fail on a downgrade
A runaway truck ramp is an emergency escape route filled with sand or gravel designed to stop a truck with failed brakes on a steep downgrade.
Question 4: What is the correct procedure for using the spring brakes when parking a CMV?
- Apply the trailer brakes only
- Chock the wheels and apply the parking brake (Correct answer)
- Leave the vehicle in gear without using the parking brake
- Apply only the service brakes and turn off the engine
Correct answer: Chock the wheels and apply the parking brake
Drivers should chock the wheels and fully apply the parking (spring) brake to prevent the vehicle from rolling while parked.
Question 5: Under federal hours-of-service rules that apply in Pennsylvania, property-carrying CDL drivers may not drive after being on duty for how many cumulative hours in 8 days?
- 60 hours
- 70 hours (Correct answer)
- 80 hours
- 55 hours
Correct answer: 70 hours
Under the 8-day/70-hour rule, property-carrying drivers may not drive after accumulating 70 on-duty hours in any 8 consecutive days.
Question 6: A CDL driver approaching a railroad crossing with no signals or gates must stop if the vehicle is carrying:
- Any cargo over 5,000 lbs
- Chlorine, even in small amounts not requiring placards (Correct answer)
- More than 10 passengers including the driver
- Livestock in enclosed trailers
Correct answer: Chlorine, even in small amounts not requiring placards
Vehicles carrying any quantity of chlorine must always stop at railroad crossings regardless of whether placards or signals are present.
Question 7: What is the primary purpose of retarder systems (Jake brakes) on commercial vehicles?
- To replace air brakes entirely on long downgrades
- To slow the vehicle and reduce wear on service brakes (Correct answer)
- To improve acceleration in heavy traffic
- To lock the drive wheels for emergency stops
Correct answer: To slow the vehicle and reduce wear on service brakes
Retarders help slow the vehicle on downgrades and in traffic, reducing heat and wear on the service brakes.
PennDOT Commercial Driver's License 3
When backing a tractor-trailer, a driver should primarily use which mirrors?