But there are many advantages to electric power such as the ability to decouple vehicle speed from engine speed, energy recapture during braking, silent operation, and no emissions when operating in electric mode. These factors add up to considerable potential energy savings.
This is why there are numerous projects aimed at developing series hybrids (the Chevy Volt being the first that comes to mind). In other words gasoline and diesel are excellent energy storage media while electric powertrains are much more efficient. So the challenge is to somehow combine the better aspects of the two in order to achieve a superior solution, and putting in place the infrastructure to support pure electric power when the energy density of batteries (or capacitors, etc) have matured sufficiently.
Right now that appears to be a revolutionary chassis combined with a small IC engine and electric drivetrain. By that I mean cars that are dramatically different and lighter than existing vehicles. Conventional designs fitted with electric power wouldn’t be nearly as much of an improvement. We should strive for major gains by thinking further outside the box.