Daimler-Chrysler is apparently working on a technology to make your car tell you when to ease off the gas.

As New Scientist reports, "The device is computerised, and combines measurements from several sources to help it judge when the car will need to start slowing down. It uses GPS to work out where it is on the road network, but its map contains far more information than those used in most satellite navigation systems for cars: it includes speed limits, gradients and road curve radii. ...[it] also has vehicle-detection radar so the driver can tell when they are getting too close to cars in front. A PC mounted in the car assimilates these measurements and predicts whether the car will need to decelerate, perhaps to take a sharp bend.
It calculates the optimum moment for the driver's foot to leave the throttle and sends a signal to a small actuator fixed under the pedal, which lightly vibrates a small piston against the underside of the pedal rubber."

Volunteer drivers who tried the system reduced fuel use by 11% on average.