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Difficulty: HardLarge Goods Vehicles (LGVs)

A Large Goods Vehicle (LGV) fitted with a mandatory speed limiter cannot exceed its set maximum speed of 56 mph (90 km/h) while travelling down a steep downhill gradient.

Answer: Answer

Answer

False
Mandatory speed limiters fitted to Large Goods Vehicles operate by restricting the fuel supply to the engine once the vehicle reaches 56 mph (90 km/h). Since the limiter does not activate the braking system, the immense mass and momentum of an LGV travelling down a steep hill can cause it to exceed 56 mph unless the driver uses auxiliary retarders, lower gears, or the service footbrake.

Step-by-Step Solution

1
Identify the operating mechanism of mandatory LGV speed limiters.
Speed limiters regulate vehicle speed solely by cutting or restricting fuel flow to the engine when the vehicle reaches 56 mph (90 km/h).
Understanding how the device controls speed is necessary to evaluate its limitations under different road conditions.
2
Analyse the forces acting on a heavy vehicle descending a steep gradient.
Gravitational force and vehicle momentum accelerate the vehicle downhill without requiring engine power.
Because speed limiters do not autonomously engage the vehicle's mechanical brakes, gravity can continue to increase the vehicle's road speed.
3
Assess the validity of the statement.
An LGV can exceed 56 mph on a descent unless the driver manually intervenes with braking systems.
The statement asserts that the vehicle cannot exceed the limit under any circumstances on a descent, which is incorrect.

Key Concept

Mechanical operation of LGV speed limiters and downhill gravitational acceleration
Estimated Time:45s
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Topics

Large Goods Vehicles (LGVs)

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