Now, I don't wish that everybody goes diving instead of driving a car, this would cause a holocaust for marine ecosystems. But ANY other product or service has the same benefit for economy. Managers and sales persons can manage or sell whatever is there. Engineers are flexible too. One of my colleges previously did automobile electronics and now he does telecommunications.
Industry makes what people buy.
If more money would be spent on other products, research efforts on other sectors could be made instead of the research efforts which are needed to achieve miniature improvements on the motor vehicle. There would be sophisticated products we can only dream of. A mobile service robot which could make household work easier, for instance. Theoretically, environmentally-friendly cars should lead to another positive feedback. With more quiet and less polluting cars, resistance against street projects should dwindle, allowing more and wider streets to be built and speed limits to go up, increasing all other problems like accidents and waste of space.