CPC Eco-Driving & Fuel Efficiency 1 — Questions and Answers
Question 1: Which driving technique most significantly reduces fuel consumption on a long motorway journey?
- Driving at the maximum speed limiter setting of 56 mph throughout
- Using cruise control to maintain a steady speed and anticipating traffic flow to avoid unnecessary braking (Correct answer)
- Driving in a lower gear at higher revs
- Using the air conditioning continuously
Correct answer: Using cruise control to maintain a steady speed and anticipating traffic flow to avoid unnecessary braking
Smooth, consistent speed — maintained using cruise control and anticipation to avoid harsh braking and acceleration — is the single biggest factor in reducing fuel consumption on motorways.
Question 2: How does tyre pressure affect fuel economy?
- Higher pressure reduces fuel economy
- Under-inflated tyres increase rolling resistance, increasing fuel consumption by up to 3% per 10% under-inflation (Correct answer)
- Pressure has no measurable effect on fuel use
- Fully inflated tyres increase fuel use due to reduced traction
Correct answer: Under-inflated tyres increase rolling resistance, increasing fuel consumption by up to 3% per 10% under-inflation
Under-inflation increases rolling resistance as more tyre sidewall is in contact with the road; this directly increases the energy (fuel) required to maintain speed.
Question 3: What does 'anticipatory driving' mean in an eco-driving context?
- Looking 5 metres ahead and reacting to hazards at the last moment
- Reading traffic situations well ahead and adjusting speed smoothly to avoid unnecessary stop-start driving (Correct answer)
- Driving faster to complete the journey before traffic builds
- Following closely to benefit from the slipstream of the vehicle ahead
Correct answer: Reading traffic situations well ahead and adjusting speed smoothly to avoid unnecessary stop-start driving
Anticipatory driving uses early perception of traffic conditions to decelerate gently and avoid braking fully, allowing momentum to be used efficiently and reducing fuel waste.
Question 4: Idling the engine of an HGV for extended periods is discouraged because:
- It damages the clutch
- It wastes significant fuel (approximately 2 litres/hour), increases emissions and can cause engine carbon build-up (Correct answer)
- DVSA prohibits idling for more than 5 minutes
- It depletes the DEF/AdBlue fluid rapidly
Correct answer: It wastes significant fuel (approximately 2 litres/hour), increases emissions and can cause engine carbon build-up
An idling HGV engine typically consumes 2–3 litres of fuel per hour, producing unnecessary CO₂ and NOx emissions; switching off when stationary for more than 2 minutes is best practice.
Question 5: What is the effect on fuel consumption of increasing motorway speed from 56 mph to 60 mph?
- Negligible — less than 1% increase
- A significant increase of approximately 10-15% due to the cubic relationship between air resistance and speed (Correct answer)
- A reduction in fuel use due to reduced journey time
- An increase of 50% due to air resistance
Correct answer: A significant increase of approximately 10-15% due to the cubic relationship between air resistance and speed
Aerodynamic drag increases with the cube of speed; a relatively small speed increase above 56 mph causes a disproportionately large increase in fuel consumption.
Question 6: How does carrying excess payload weight above the planned load affect fuel consumption?
- It reduces fuel consumption through improved grip
- Every extra tonne increases fuel consumption by approximately 1-2%, increasing running costs and emissions (Correct answer)
- Weight has no measurable effect on fuel consumption
- Only affects fuel consumption on hills
Correct answer: Every extra tonne increases fuel consumption by approximately 1-2%, increasing running costs and emissions
Extra weight directly increases the engine's workload on hills and in acceleration, increasing fuel consumption; careful load planning to avoid deadweight reduces operating costs.
CPC Eco-Driving & Fuel Efficiency 1
Which driving technique most significantly reduces fuel consumption on a long motorway journey?