Environmentally friendly driving and fuel economy
This domain tests whether you can explain and demonstrate economical driving with a heavy vehicle: the physics of resistance, the correct use of gears and auxiliary brakes, and the operational habits that cut fuel and emissions.
Where the fuel goes
A lorry fights rolling resistance, aerodynamic drag, gradient and acceleration. Aerodynamic drag rises with the square of speed, so the step from 80 to 90 km/h adds roughly a quarter more air resistance and a noticeable fuel penalty on that stretch. Weight and under-inflation add rolling resistance. Idling burns fuel for nothing - a heavy engine can use well over a litre an hour standing still, and Danish rules restrict unnecessary idling, so switch off where the vehicle is stationary and not in a traffic queue.
Technique
- Accelerate briskly to the desired speed and shift up early, using the engine's torque band rather than revving.
- Read the road far ahead: lift off early for a red light rather than braking late, and keep momentum where it is safe.
- Use cruise control on steady motorvej running, but not on hilly roads where it holds throttle unnecessarily.
- Use the retarder and engine braking on descents - fuel cut-off means zero consumption while the engine is being driven.
- Plan the route and the load: fewer kilometres, no detours, no unnecessary weight, correct tyre pressures, aerodynamic aids kept intact.
Emissions equipment
Euro VI engines use SCR with AdBlue to cut NOx, and a particulate filter for soot. Short-town running and long idling prevent regeneration and cause faults. Running out of AdBlue derates power.
Worked example. A driver covers 300 km a day at 90 km/h instead of the lorry's 80 km/h limit. Air resistance rises by (90/80)² = 1.27, about 27 percent more drag, which typically translates into roughly a tenth more fuel on that section - a few litres a day, well over a thousand litres a year. The reasoning: drag dominates at speed, so the last few km/h are the most expensive ones you can buy.
Traps that cost marks
- Claiming that a higher gear always saves fuel while the engine is labouring.
- Ignoring tyre pressure as a fuel factor.
- Forgetting that retarder use on a descent means the engine is consuming no fuel at all.