Federal fuel economy standards languished in Congress, and average vehicle mileage dropped to its lowest level in decades, but the Prius showed people that another way is possible.

Nor is it certain that the scheme provides a more general boost to the economy, as buyers may have been put off other purchases in order to afford a new vehicle.

The bus Train, a dual-mode vehicle that has the versatility of a bus, the speed of light rail and fuel economy vastly better than either.