DTT HGV Vehicle Inspection and Load Securing 3 — Questions and Answers
Question 1: How should a truck driver check the coupling between a tractor unit and trailer?
- Check the fifth-wheel lock engagement, safety catch is secured, trailer kingpin seated correctly, and perform a 'pull-test' by moving forward gently against the brakes (Correct answer)
- Check the kingpin is inserted and continue — couplings are self-locking
- Check visually from the cab using mirrors
- Only needed when coupling after a trailer has been on the ground more than 2 hours
Correct answer: Check the fifth-wheel lock engagement, safety catch is secured, trailer kingpin seated correctly, and perform a 'pull-test' by moving forward gently against the brakes
Coupling check: confirm the kingpin is locked in the fifth wheel, the safety catch is engaged, airlines and electrical connections are correctly made, and perform a pull-test with the trailer brakes applied to confirm lock.
Question 2: What is the tyre tread depth minimum for a commercial vehicle (truck or bus)?
- At least 1mm across 75% of the tread width and around the full circumference (Correct answer)
- 1.6mm — same as for private cars
- 2mm across the full tread width
- No minimum for commercial vehicles — condition is the standard
Correct answer: At least 1mm across 75% of the tread width and around the full circumference
Commercial vehicles (trucks and buses) require a minimum tread depth of 1mm across at least 75% of the tread width and around the entire circumference of the tyre.
Question 3: What must a driver check regarding the trailer air lines (susie hoses) before moving off?
- That both red (emergency) and yellow (service) airlines are correctly coupled, undamaged, and secure — not dragging on the ground (Correct answer)
- Only the red airline needs checking — yellow is optional
- Airlines are checked only by the workshop, not the driver
- Visually confirm they are connected — no further check needed
Correct answer: That both red (emergency) and yellow (service) airlines are correctly coupled, undamaged, and secure — not dragging on the ground
Both the red (emergency/supply) and yellow (service/brake) airlines must be correctly connected to the trailer, not damaged or kinked, and positioned so they do not drag or snag when turning.
Question 4: During a walkaround check, a driver notices the trailer's tail lights are not working. What should they do?
- Report the defect and do not depart until tail lights are repaired — operating without tail lights at night or in poor visibility is dangerous and illegal (Correct answer)
- Continue the journey in daylight only
- Attach reflective triangles to substitute for missing lights
- Use hazard lights as a substitute while seeking repair
Correct answer: Report the defect and do not depart until tail lights are repaired — operating without tail lights at night or in poor visibility is dangerous and illegal
Non-functioning tail lights make the vehicle invisible from behind at night or in poor visibility — an extreme danger and a serious roadworthiness defect. The vehicle must not be driven until repaired.
Question 5: What is the correct procedure for checking a bus's emergency exits before starting a service?
- Check all emergency exits open easily from inside and outside, are unobstructed, and have visible emergency exit signs and working emergency hammers (Correct answer)
- Check the main door only — emergency exits are checked at CVRT only
- Emergency exits are checked weekly during depot inspections
- Check that emergency exit signs are lit — physical exit testing is not required
Correct answer: Check all emergency exits open easily from inside and outside, are unobstructed, and have visible emergency exit signs and working emergency hammers
All emergency exits (doors, roof hatches, windows) must open freely from inside and outside, not be obstructed by luggage or equipment, have visible signage, and emergency hammers must be present and accessible.
Question 6: What is the 'PMTM' (Permissible Maximum Technical Mass) of a vehicle?
- The maximum weight the vehicle is designed and engineered to carry — cannot legally be exceeded (Correct answer)
- The payload capacity without passengers
- The maximum weight permitted on a specific road or bridge
- The weight of the vehicle fully loaded including fuel and driver
Correct answer: The maximum weight the vehicle is designed and engineered to carry — cannot legally be exceeded
PMTM (also called Maximum Authorised Mass or GVW) is the maximum weight for which the vehicle is designed. Exceeding it is illegal, invalidates insurance, and creates dangerous handling and brake performance.
DTT HGV Vehicle Inspection and Load Securing 3
How should a truck driver check the coupling between a tractor unit and trailer?