Originally posted on 7 Mar 2009:
In a nutshell, ecodriving is driving in the most economical way possible: it starts with brisk acceleration (trying to use the peak torque of the engine) so you get to "cruising" speed fairly quickly, and then trying to use a minimum of throttle to maintain the speed. Obviously, uphills are your biggest challenge, where it takes throttle just to maintain speed -- if you can, it helps if you let yourself lose a little speed up hills.
Then use the downhills to ease way off the throttle, or if you need to carry speed, put it in neutral and coast (with the engine idling) -- at 60mph at idle in my xA, I get over 300mpg while coasting. I've found it is best to put the car back into gear right before the bottom of the hill, and use a little throttle to carry the speed that you've gained up the next hill, or onto the flat road. This is the corollary to losing speed while going up: gain some speed while going down, and use it to your best advantage.
The other common situation is when you can coast, but you need to slow down, or will soon come to a stop -- then you should downshift into a lower gear. When the engine is being pushed by the wheels, in almost all modern fuel injected cars -- will completely shut off the fuel to the engine; yielding "infinite" mileage for the duration of this kind of coasting. I try to only use my brakes at the very end of the coast right before you stop.
So, if you only use just enough throttle to get you where you need to go, and try not waste energy by heating the brakes; but instead use it to shut off fuel to the engine, and coast to carry speed whenever you can, carrying momentum as far as you can -- then you are most of the way to good ecodriving technique. In hybrid cars, this is when you can use regenerative braking to regain some of the energy you used while accelerating. Without the electrical regenerative braking though, the best we can do is use this energy to be able to stop burning any more fuel while slowing the car down.
There are other things to try, like pulse and glide (when on flat-ish terrain), and minimizing your use of A/C -- and of course if you want to try some simple and reversible modifications: like pumping up your tires a bit above the recommended pressure – up to the maximum pressure listed on the sidewall, or some of the aerodynamic modifications on the grill, etc., then all the better.