"Coasting or gliding[edit]

An alternative to acceleration or braking is coasting, i.e. gliding along without propulsion. Coasting dissipates stored energy (kinetic energy and gravitational potential energy) against aerodynamic drag and rolling resistance which must always be overcome by the vehicle during travel. If coasting uphill, stored energy is also expended by grade resistance, but this energy is not dissipated since it becomes stored as gravitational potential energy which might be used later on. Using stored energy (via coasting) for these purposes is obviously more efficient than dissipating it in friction braking.

When coasting with the engine running and manual transmission in neutral, or clutch depressed, there will still be some fuel consumption due to the engine needing to maintain idle engine speed. While coasting with the engine running and the transmission in gear, most cars' engine control unit with fuel injection will cut off fuel supply, and the engine will continue running, being driven by the wheels. Compared to coasting in neutral, this has an increased drag, but has the added safety benefit of being able to react in any sudden change in a potential dangerous traffic situation, and being in the right gear when acceleration is required.[citation needed]
Coasting with a vehicle not in gear is prohibited by law in most US states. An example is Maine Revised Statues Title 29-A, Chapter 19, §2064 "An operator, when traveling on a downgrade, may not coast with the gears of the vehicle in neutral.

Turning the engine off instead of idling does save fuel. Traffic lights are in most cases predictable, and it is often possible to anticipate when a light will turn green. Some traffic lights (in Europe and Asia) have timers on them, which assist the driver in using this tactic.

Some hybrids must keep the engine running whenever the vehicle is in motion and the transmission engaged, although they still have an auto-stop feature which engages when the vehicle stops, avoiding waste. Maximizing use of auto-stop on these vehicles is critical because idling causes a severe drop in instantaneous fuel-mileage efficiency to zero miles per gallon, and this lowers the average (or accumulated) fuel-mileage efficiency." (http://en.wikipedia.org/wiki/Energy-efficient_driving )

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"Coasting may refer to:

– Performing a natural deceleration of a motor when the power is removed; a type of fuel economy-maximizing behavior" (http://en.wikipedia.org/wiki/Coasting )

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Autowoordenboek.nl, Deel 2 Nederlands-Engels / Henk Wagenaar Hummelinck:
• uitrollen van auto in vrijloop = coast; freewheel

Autowoordenboek.nl, Deel 1 Engels-Nederlands / Henk Wagenaar Hummelinck:
• coast (ww.; Am) = freewheelen; uitrollen met uitgeschakelde aandrijving
• coasting clutch = freewheel; vrijloopkoppeling