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Is it more efficient to drive at a constant speed or accelerate, neutral, and repeat?

thanks

Public Comments

1. constant i suggest cruise control. accelerating too often wastes your gas
2. Driving at a constant speed is the most efficient way to travel. You can coast in neutral down hills, if it's easy for you, but on flat / uphill surfaces, being consistent is far better for your mileage. Can't beat the cruise control for this.
3. A constant speed.
4. Constant speed. The power required to overcome air resistance goes as the cube of the speed -- which should tell you a lot.
5. Driving at a constant speed will save gas. Changing gears and accelerating will use up more gas even if you decelerate after accelerating.
6. Depends on how much of an mpg fanatic you are. The winners in an mpg contest about 30 years ago, driving a radically modified Mercedes(?), would coast with engine off until their speed was just a few mph, then engage the clutch in the highest gear and floor the accelerator until they reached 35 or so. Then they'd disengage the clutch and switch the engine off for another cycle. The low rpm's and full throttle minimized engine pumping and windage losses. The car had high-pressure skinny knife-edge tires and a very streamlined body, and won with ~400 mpg! When you include very hilly terrain, all of that cruise control/constant-speed worship makes no sense. Any time your engine or brakes are preventing you from going as fast downhill as you would if coasting, you're wasting gas (unless it's regenerative braking). Those 100-mph 18-wheelers aren't doing it to scare you, they're just saving fuel. Has anybody heard of a roller coaster?