LGV Safe Braking Distances 3

Question 1

What additional braking distance must an LGV driver allow when driving with a trailer in a 'jack-knife' risk situation?

Accepted Answer

Increase following distance significantly and brake progressively — jack-knife prevention requires gentle brake application

Answer

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?

Accepted Answer

50 mph

Answer

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)?

Accepted Answer

96 metres (315 feet)

Answer

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?

Accepted Answer

Ice can multiply stopping distances by up to 10 times compared to dry conditions

Answer

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?

Accepted Answer

Using the engine's compression resistance by selecting a low gear to slow the vehicle without brake application

Answer

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.

UK LGV Theory Practice Test

UK LGV Theory Practice Test

LGV Safe Braking Distances 3