PCV Skid Prevention and Defensive Driving 2 — Questions and Answers
Question 1: What effect does a fully loaded bus have on its cornering stability compared to an empty bus?
- A full bus corners more safely because of lower centre of gravity
- A full bus has a higher centre of gravity, increasing rollover risk in fast cornering (Correct answer)
- Load has no effect on cornering stability
- A full bus brakes faster so corners are less hazardous
Correct answer: A full bus has a higher centre of gravity, increasing rollover risk in fast cornering
A fully loaded bus raises the centre of gravity, increasing the risk of rollover when cornering too fast.
A double-deck bus with a full upper deck has a higher centre of gravity than when empty. Combined with the vehicle's height, this significantly increases rollover risk when taking corners at excessive speed. Drivers must reduce speed well before bends and roundabouts. The risk is highest on cambered or uneven road surfaces.
Question 2: What is 'aquaplaning' and how should a PCV driver respond if it occurs?
- Aquaplaning is overheating of brakes; the driver should stop and cool the brakes
- Aquaplaning is when tyres ride on a water film and lose contact with the road; ease off the accelerator gently and avoid braking (Correct answer)
- Aquaplaning is a form of tyre blowout; brake gently and pull over
- Aquaplaning is condensation on windows; open vents to clear it
Correct answer: Aquaplaning is when tyres ride on a water film and lose contact with the road; ease off the accelerator gently and avoid braking
Aquaplaning occurs when tyres float on a water film; the driver should ease off the accelerator gradually and avoid sharp steering or braking.
Aquaplaning happens when a vehicle is travelling fast enough on a flooded road that tyre tread cannot clear water quickly enough, causing the tyre to ride on a film of water and lose grip. The driver should ease gently off the accelerator (not brake suddenly), hold the steering lightly, and wait for grip to return as speed drops. Sudden inputs can cause a skid or spin.
Question 3: How does the weight of standing passengers on a single-deck bus affect braking?
- It has no effect on braking performance
- It reduces braking performance due to increased inertia, requiring greater stopping distances (Correct answer)
- Standing passengers improve stability and shorten stopping distance
- The automatic braking system adjusts for passenger load automatically
Correct answer: It reduces braking performance due to increased inertia, requiring greater stopping distances
Extra passenger weight increases the vehicle's inertia, meaning it takes longer to stop — the driver must allow more room.
A heavier vehicle has greater kinetic energy at any given speed and therefore requires more braking force and distance to stop. Standing passengers add significant mass high up in the vehicle. PCV drivers must account for vehicle load when judging safe following distances and approach speeds, and must drive smoothly to avoid passengers falling.
Question 4: Which of the following best describes the 'limit point' technique for approaching bends?
- The furthest visible point along the road; if it is not moving away, the driver is going too fast (Correct answer)
- The point at which the driver must begin sounding the horn
- The nearest visible point of the road; the driver should accelerate once it is reached
- The GPS waypoint indicating the bend location
Correct answer: The furthest visible point along the road; if it is not moving away, the driver is going too fast
The limit point is the furthest visible point of the road; if it appears stationary or moving closer, the vehicle is too fast for the visibility available.
The limit point technique involves watching the furthest point to which the driver can see along the road ahead. On a bend, if the limit point appears to move towards the driver, they are travelling too fast for the available stopping distance within their line of sight. The driver should reduce speed until the limit point moves away again. This is particularly important for large, high-clearance vehicles like buses.
Question 5: When driving on ice or packed snow, which technique should a PCV driver use to avoid skidding while braking?
- Stamp hard on the brakes to lock the wheels
- Apply the brakes progressively and gently, allowing ABS to function if fitted (Correct answer)
- Use only the handbrake to stop
- Brake only with the engine by rapidly downshifting multiple gears
Correct answer: Apply the brakes progressively and gently, allowing ABS to function if fitted
Progressive, gentle braking allows ABS (if fitted) to operate effectively and avoids wheel lock on slippery surfaces.
On ice or snow, smooth, progressive brake application is essential. Modern buses with ABS allow the driver to apply firm, continuous pressure — the ABS will automatically modulate brake pressure to prevent wheel lock. Without ABS, very gentle, progressive pressure should be used. Harsh braking locks wheels immediately on ice, leading to loss of steering control.
Question 6: What is the effect of a crosswind on a high-sided vehicle such as a double-deck bus?
- Crosswinds push the vehicle closer to the kerb, improving stability
- Crosswinds can cause the vehicle to be pushed off course, requiring steering correction (Correct answer)
- High-sided vehicles are unaffected by crosswinds due to their weight
- Only open-top buses are affected by crosswinds
Correct answer: Crosswinds can cause the vehicle to be pushed off course, requiring steering correction
Crosswinds exert lateral force on the large surface area of a double-deck bus, pushing it off course.
High-sided vehicles have large surface areas that act as a sail in crosswinds. A sudden strong gust — particularly when emerging from a sheltered area — can push the bus significantly off line. Drivers should grip the steering wheel firmly, anticipate exposed sections (bridges, gaps in hedges), and reduce speed in very windy conditions.
PCV Skid Prevention and Defensive Driving 2
What effect does a fully loaded bus have on its cornering stability compared to an empty bus?