Turns out, your car's engine is useless about a third of the time when you're driving. Bosch is using that math to estimate that the newest generation of its stop-start system could cut a car's overall fuel use by about 10 percent.
When drivers set out to hypermile, there is a spectrum of techniques that they can use. These range from the good - don't blast away from a red light and don't speed up then slam on the brakes at the next red - to the risky. Dale Earnhardt, Jr. may be able to use hypermiling tricks like shutting down the engine at high speeds to win a race, but that doesn't mean you should try it during your commute.