There are situations however where you can actually save gas in total gallons, such as the following technique:

1) Choose alternate routes based on traffic signals at the time. This works well on a grid where you need to go say 5 blocks east, and 8 blocks north. Let's say I would normally turn left at a particular light. If the arrow to turn left is red, but the signal to go straight is still clear, I'm better off going forward then going left two blocks later, when I happen to reach a left-hand turning lane with a green arrow. Conversely, if the light is red to go straight, and the left arrow is green, it's better off to go left earlier, to avoid stopping (this is assuming a fairly constant distance for each route, as would be the case on a grid). Even on non-grdided layouts, you can use this technique by knowing back routes and things like that. I can actually arrive at a destination faster and use less gas, as opposed to going the same path all the time, if there are multiple alternate paths of the same length, by avoiding the stops.

2) Anticipate traffic lights. This way, if you a green light up ahead is about to turn red before you reach it, let off the gas and coast from as far back as possible. Some people will be impatient, race past you, and brake to a stop ahead of you. On traffic signals which are triggered by sensors (on major thoroughfares, lights are kept green by default unless there are people waiting to turn), allowing people to do this works in your favor, as they trigger the light, and by the time you get there, you are still moving and only have to go from say 25 - 50mph instead of 0-50mph.

On lights with sensors, you can tell if a red light is about to turn green as well if the cars approaching the intersection from the cross-street are beginning to slow down (this means their light is yellow) AND there are no cars waiting to turn left. If there are cars waiting you turn left, you known the light will stay red to allow them a protected turn, so you're better off trying to get regenerative braking. If there are no cars in the turning lanes, it will turn green soon, so you're better off keeping your momentum up than charging the battery. No matter what though, make sure you have enough room to stop safely if you misjudge the situation.

If the stop-lights were actually linked, they could do all this judgment with a centralized system and maximize the fuel efficiency for everyone by using smarter timing on the lights. That may even have a significant benefit on smog, as well as average commute time in the city if they could get a significant improvement.