Other satnav makers are already focusing more on fuel economy. Econav, which is unconnected with Bosch's product, was launched last year by the Spanish company Vexia, based in Madrid, Spain. It asks users to specify their car type and number of passengers so it can better gauge when a driver should change gear or reduce acceleration.

David Elder, U.K. country manager for Vexia, is skeptical that the information collected by Bosch's software will make much difference. "I would think the optimum route would be the same for whatever vehicle you are driving," he says.

This may be true for short journeys, says Meyer, but the system will suggest different routes for longer trips. According to Meyer, ECO2 will go into production this summer and will be integrated into the dashboard navigation systems of a number of cars, but he would not specify which makes or models.

John Holland, CEO of Journey Dynamics, a traffic technology company based in Guildford, U.K., says that avoiding traffic will affect fuel consumption more dramatically because a continuously moving vehicle does not accelerate as much as a vehicle in stop-and-go traffic. But by far, says Holland, the biggest influence on fuel consumption is driver behavior. Giving a driver feedback when they are overaccelerating can markedly influence the amount of fuel they use, he notes. Meyer agrees that driver behavior is a major factor, and says Bosch is working on this too.

Holland also believes that the 9 percent increase in journey time is unnecessary. "There's good evidence that driving economically doesn't necessarily mean a longer journey time. It doesn't mean having to drive like a granny at 40 miles per hour down the motorway."