This works well on manual transmissions. When you know you'll be slowing, i.e. you can see the light well ahead turn yellow, just take your foot off the gas, shift into neutral and gently coast on until you need to stop. There's no sense speeding to a stop light and wasting perfectly good momentum in the process. Odds are the light may even turn green again by the time you get to it.
Similarly, when cresting a hill, so long as the road ahead is safely clear, let gravity do the work instead of your engine. When slowing while going up a hill, again, let gravity do the work.
by Jabber on September 19 2008
this tip works for 55% of voting Fuelly members.