LGV Safe Braking Distances 3 — Questions and Answers
Question 1: What additional braking distance must an LGV driver allow when driving with a trailer in a 'jack-knife' risk situation?
- Increase following distance significantly and brake progressively — jack-knife prevention requires gentle brake application (Correct answer)
- Brake harder and faster to prevent jack-knife
- Only worry about jack-knife on icy roads
- Reduce speed and use the trailer brake lever independently
Correct answer: Increase following distance significantly and brake progressively — jack-knife prevention requires gentle brake application
Jack-knife occurs when the trailer pushes around the tractor unit due to overbraking or slippery conditions. Prevention requires progressive braking (not harsh), maintaining trailer alignment, and using EBS/ABS systems. Increasing following distance reduces the need for emergency stops.
Question 2: At what road speed does thinking distance equal approximately 15 metres?
- 50 mph (Correct answer)
- 30 mph
- 60 mph
- 40 mph
Correct answer: 50 mph
At 50 mph, thinking distance is approximately 15 metres (the Highway Code uses a 0.67 second reaction time as standard). At higher speeds, thinking distance increases linearly with speed.
Question 3: What is the total stopping distance at 70 mph in ideal dry conditions (car basis)?
- 96 metres (315 feet) (Correct answer)
- 73 metres
- 120 metres
- 80 metres
Correct answer: 96 metres (315 feet)
At 70 mph, the Highway Code gives a total stopping distance of approximately 96 metres (315 feet): 21 metres thinking distance plus 75 metres braking distance. For an LGV at 60 mph (their maximum), stopping distances will be considerably greater.
Question 4: How does icy road conditions affect braking distance compared to dry conditions?
- Ice can multiply stopping distances by up to 10 times compared to dry conditions (Correct answer)
- Ice doubles stopping distance
- Ice increases stopping distance by 25%
- Ice only affects steering, not braking distance
Correct answer: Ice can multiply stopping distances by up to 10 times compared to dry conditions
On ice, the friction between tyres and road can be near zero. Stopping distances can increase up to 10 times compared to dry conditions. Even ABS cannot overcome the fundamental lack of grip — only extreme speed reduction prevents accidents on icy roads.
Question 5: What is engine braking and how does it help LGV drivers on descents?
- Using the engine's compression resistance by selecting a low gear to slow the vehicle without brake application (Correct answer)
- Using the engine to power the brakes electronically
- Applying the footbrake while in a high gear
- Using the engine's turbocharger to slow the vehicle
Correct answer: Using the engine's compression resistance by selecting a low gear to slow the vehicle without brake application
Engine braking uses the engine's resistance to rotation to decelerate the vehicle when the throttle is released. For LGVs on long descents, selecting a lower gear before the descent uses engine braking to control speed without continuously applying the footbrakes, preventing brake fade.
Question 6: What does an LGV driver do differently from a car driver in terms of anticipation to compensate for longer stopping distances?
- Reads the road further ahead, identifies hazards earlier, and creates larger gaps to allow for the vehicle's extended stopping distance (Correct answer)
- Drives at lower speeds at all times
- Uses ABS more frequently to compensate
- Relies on air brakes as they are more powerful than car brakes
Correct answer: Reads the road further ahead, identifies hazards earlier, and creates larger gaps to allow for the vehicle's extended stopping distance
Professional LGV drivers are trained in advanced anticipation: looking well ahead for developing hazards (12+ seconds), identifying hazards early enough to respond with gradual speed reduction rather than emergency braking, and maintaining large following distances at all times.
LGV Safe Braking Distances 3
What additional braking distance must an LGV driver allow when driving with a trailer in a 'jack-knife' risk situation?