"Only about 15% of the energy from the fuel you put in your tank gets used to move your car down the road or run useful accessories, such as air conditioning. The rest of the energy is lost to engine and driveline inefficiencies and idling."
I don’t have the time or knowledge to know how accurate those figures are, but even if that’s exagerated, it’s clear that a lot of energy is lost (and therefore fuel used) when a car is not actually moving.
If more car manufacturers were on the ball, they’d be working on similar things (or licensing the technology from Citroen). This would be win for them because they can continue selling cars to a public that is ever more conscious of rising fuel prices, and a win for buyers because of the reduced fuel usage, and a win for an environment through reduced emissions (and less demand for fuel).
This kind of “rethinking” of processes, of the way things are done, is essential to create a sustainable future. We don’t (necessarily) need to go “backwards” or without certain things to live sustainably – often it only takes a bit of energy to rethink how we do things to get impressive gains.