LGV Safe Braking Distances 2 â Questions and Answers
Question 1: How does an unladen LGV compare to a fully loaded LGV in terms of braking?
- An unladen LGV can brake harder but may experience wheel lock-up more easily â load improves tyre adhesion (Correct answer)
- An unladen LGV always stops shorter than a loaded one
- A loaded LGV stops shorter due to increased tyre grip
- There is no significant difference
Correct answer: An unladen LGV can brake harder but may experience wheel lock-up more easily â load improves tyre adhesion
An unladen LGV has less mass but also less tyre contact force, making wheels more susceptible to locking. A loaded LGV has more mass (longer stopping distance) but better tyre adhesion. Both situations require careful brake application.
Question 2: What is the effect of excessive speed on braking distance?
- Doubling speed quadruples braking distance â the relationship is exponential, not linear (Correct answer)
- Doubling speed doubles braking distance
- Speed has a linear effect on stopping distance
- Speed affects thinking distance only
Correct answer: Doubling speed quadruples braking distance â the relationship is exponential, not linear
Braking distance increases with the square of speed (kinetic energy = œmv²). Doubling speed from 30 to 60 mph increases braking distance by a factor of four. This exponential relationship is why high speed is so dangerous for heavy vehicles.
Question 3: What is 'aquaplaning' and how should an LGV driver respond?
- When a layer of water builds up under tyres causing loss of steering and braking â ease off throttle, avoid sharp steering or braking (Correct answer)
- When brakes lock on a wet road
- When the vehicle skids in deep standing water
- When spray from other vehicles reduces visibility
Correct answer: When a layer of water builds up under tyres causing loss of steering and braking â ease off throttle, avoid sharp steering or braking
Aquaplaning occurs when a tyre rides on a layer of water and loses contact with the road surface. There is no steering or braking control. The driver should ease off the throttle gently, avoid steering or braking sharply, and wait for speed to reduce and tyres to regain contact.
Question 4: How does tyre tread depth affect braking distance on a wet road?
- Worn tyres have reduced ability to channel water away, significantly increasing wet stopping distances (Correct answer)
- Tyre depth has minimal effect on stopping distance
- Only front tyre depth matters for braking
- Deeper tread always reduces stopping distance in all conditions
Correct answer: Worn tyres have reduced ability to channel water away, significantly increasing wet stopping distances
Tyre tread channels water away from the contact patch. As tread wears, its ability to disperse water reduces, causing the tyre to aquaplane at lower speeds and stopping distances to increase dramatically on wet roads.
Question 5: What is the emergency stopping technique for an LGV with ABS?
- Apply full brake pressure firmly and maintain it â ABS prevents wheel lock and allows steering (Correct answer)
- Pump the brakes to prevent lock-up
- Apply brakes progressively to the threshold
- Apply the handbrake simultaneously for maximum deceleration
Correct answer: Apply full brake pressure firmly and maintain it â ABS prevents wheel lock and allows steering
With ABS, the driver should apply maximum brake pressure firmly and hold it. The ABS system automatically prevents wheel lock-up by modulating brake pressure. Pumping the brakes overrides ABS and reduces effectiveness.
Question 6: Why are empty tankers particularly challenging to stop safely?
- Empty tankers can have liquid residue that surges, and lower mass means wheels lock more easily (Correct answer)
- Empty tankers are lighter, so they always stop shorter
- Empty tankers have identical braking characteristics to loaded ones
- Empty tankers are prohibited from motorways due to braking issues
Correct answer: Empty tankers can have liquid residue that surges, and lower mass means wheels lock more easily
Tankers carrying any residual liquid have a free surface effect â liquid moves and shifts the vehicle's centre of gravity. Additionally, the lower overall weight increases the risk of wheel lock-up. Drivers must be extra cautious and allow extra stopping distance.
LGV Safe Braking Distances 2
How does an unladen LGV compare to a fully loaded LGV in terms of braking?