LGV Safe Braking Distances 1 — Questions and Answers
Question 1: What is the overall stopping distance for a vehicle travelling at 60 mph in ideal conditions (thinking distance plus braking distance)?
- 73 metres (240 feet) (Correct answer)
- 55 metres
- 91 metres
- 60 metres
Correct answer: 73 metres (240 feet)
At 60 mph, the thinking distance is approximately 18 metres and the braking distance approximately 55 metres, giving an overall stopping distance of around 73 metres (240 feet) in ideal conditions. For a loaded LGV, this will be significantly greater.
Question 2: How does vehicle weight affect braking distance for an LGV?
- Greater weight increases kinetic energy, requiring significantly longer distances to stop (Correct answer)
- Greater weight improves traction, reducing stopping distance
- Weight has minimal effect on modern air-braked vehicles
- Heavier vehicles stop faster due to increased tyre contact area
Correct answer: Greater weight increases kinetic energy, requiring significantly longer distances to stop
Kinetic energy increases with mass. A fully loaded LGV has vastly more kinetic energy than a car at the same speed and requires proportionally greater braking distances. This is why LGV drivers must maintain much larger following distances.
Question 3: What effect does a wet road surface have on braking distance?
- It typically doubles the braking distance compared to a dry road (Correct answer)
- It increases braking distance by 25% only
- It has minimal effect on air-braked vehicles
- It only affects front wheel braking
Correct answer: It typically doubles the braking distance compared to a dry road
A wet road surface approximately doubles stopping distances because the water film between the tyre and road surface reduces friction (grip). LGV drivers must double their following distance in wet conditions.
Question 4: What is 'thinking distance' in the context of stopping distance?
- The distance the vehicle travels during the driver's reaction time before the brakes are applied (Correct answer)
- The distance travelled once the brakes are applied
- The time taken to decide to brake
- The distance a vehicle skids after maximum braking
Correct answer: The distance the vehicle travels during the driver's reaction time before the brakes are applied
Thinking distance is the distance covered from the moment a driver perceives a hazard to the moment they begin to apply the brakes. At 60 mph, a driver travels approximately 18 metres during a typical reaction time of 0.67 seconds.
Question 5: What is brake fade and how does it affect LGV braking?
- Reduced braking efficiency caused by heat build-up in brake components — especially dangerous on long descents (Correct answer)
- Brakes wearing out over time
- ABS disengaging during heavy braking
- Loss of air pressure in the brake system
Correct answer: Reduced braking efficiency caused by heat build-up in brake components — especially dangerous on long descents
Brake fade occurs when friction materials and brake drums or discs overheat, reducing their ability to generate friction. For LGVs on long descents, continuous brake application generates extreme heat. Engine braking and gear selection are essential to prevent brake fade.
Question 6: What is the recommended following distance for an LGV at 60 mph on a dry motorway?
- At least a 2-second gap — but significantly more due to the vehicle's weight and longer stopping distance (Correct answer)
- Exactly 2 seconds — the same as for any vehicle
- 1 second per 10 mph (6 seconds at 60 mph)
- 50 metres minimum
Correct answer: At least a 2-second gap — but significantly more due to the vehicle's weight and longer stopping distance
The 2-second rule gives a minimum for cars, but heavily loaded LGVs have far longer stopping distances. Professional LGV drivers are trained to maintain much greater gaps — often 4-6 seconds or more — because their stopping distances can be 2-3 times longer than cars.
LGV Safe Braking Distances 1
What is the overall stopping distance for a vehicle travelling at 60 mph in ideal conditions (thinking distance plus braking distance)?