> Huh. I remember my dad telling me faster speeds are actually *better* for gas mileage. But I may be confusing that with highway versus town driving.

The optimal speed for fuel effeciency varies by car, but it's generally somewhere around 55 mph. There are a lot of different factors that influence your ideal speed, including your car's weight, engine, transmission, tires, and what sort of accessories (air conditioning, stereo, etc.) you have running.

In that sense, faster speeds are better than slower speeds (going 5 mph would get you terrible mileage, for instance), but only up to a point. Once you achieve maximum effeciency in your top gear, going faster will lower your effeciency.

Stop and go traffic is the worst, because you waste a lot of energy getting a car up to speed in the first place, and then you lose all the energy you had when you brake (unless you have a hybrid, in which case you get to keep some of it).

Another interesting thing worth considering is the weight of your car. You can get better mileage by having less weight in your car. One thing that adds weight that you have control over is the amount of gas in your tank. It's pretty negligible, but if you never fill your tank more than half full, you will be more effecient. Of course you have to balance this against the value of your time spent gassing up more frequently and in a market where gas prices are rising it's best to buy lots of gas whenever you can, before prices go up further (the opposite is true if prices are falling).

Stephen