[Double Tap]

If there are any hills, and you are going under 5mph, shut off the engine on the downhills and roll. Even if a few cars cut in front of you, you will conserve gas if you can keep your engine off for more then 45 seconds or so (someone want to correct that time range).

Good way to have an accident and make a bad situation worse. Why? Because I would bet that 99% of the vehicles on the road are running power steering and power brakes. They don't work well without the engine running.

[CharlesWayneCT]

OK, I revoke that bad suggestion. I've never done it in an automatic transmission before -- in a manual, you just use the clutch for most braking at those speeds.

[L,TOWM]

Not to mention a lot of cars with auto trannies won't even start without being in "Park".

Bad setting to move your gear selector to in a moving vehicle with an automatic transmission.