On a long descent, a driver shifts into neutral to coast and save fuel. Why is this regarded as poor and unsafe practice?

Why A is correct

In neutral, the engine contributes nothing to slowing the vehicle, so gravity accelerates you down the grade unopposed except by the friction brakes — the same brakes that fade when used continuously. Engine braking in gear is the steady, heat-free drag that keeps a descent at a chosen speed; removing it means building speed you must then shed with a system that may be overheating. Coasting also leaves you a half-second behind any emergency, because re-engaging a gear costs time you will not have if a deer, a stalled car or gravel appears below the crest.

Why the other options are wrong

B. Because neutral damages the transmission on modern vehicles

Transmission wear is a maintenance argument, not the safety issue. The reason coasting is poor practice on a grade is what happens to your speed control and your braking reserves, not what happens to the gearbox.

C. Because neutral disables the power steering on most cars

Power steering is driven by the engine, not the gear selector, and it keeps working in neutral with the engine running. The real loss from coasting is the engine's braking contribution, which is a braking-system matter.

D. Because coasting is illegal only for vehicles over a certain weight

Weight-based rules are irrelevant here: the physics of gravity, gears and brake heat applies identically to a hatchback and a lorry, and the practice is discouraged for every vehicle on every grade.

On the road

A canyon descent you know well: one driver ahead coasts in neutral, lights up the brakes twice on the straights, and drifts into the hairpin visibly faster than the corner wanted. You take the same descent in third, engine dragging, brakes touched twice lightly. At the bottom, his pedal is going soft and yours is exactly as it was at the top — the whole difference is one gear choice.

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