A more likely scenario seems to be a combination of mass transit system for travel into and around cities, with small 'loe emission' cars for urban use and larger hybrid or lean burn cars for use elsewhere. Electronically tolled highway might be used to ensure that drivers pay charges geared to actual road use. Better intergration of transport system is also highly desirable - and made more feasible by modern computers. But these are solutions for countries which can afford them. in most developing countries, old cars and old technologies continue to predominate.