Electric Transportation System
The only way to make transportation sustainable is to make it almost completely electric. Since oil comprises 98% of the fuel for the current transportation system (cars, trucks, diesel rail, planes, and ships), this will be quite a task. The Renewable Energy System can provider the electricity, but to remake the transportation system will require a large-scale change in the vehicles used, the infrastructure built, and perhaps most importantly but least understood, in the way cities and towns are laid out.
A continent-sized electric transportation system will have to be based on the original, that is, one based on rail. Electric high-speed rail is actually the most recent innovation for a major mode of transportation. High-speed rail will have to replace most airline travel, since planes can not possibly be electric. A sustainable plane fleet would have to use sustainably-harvested biomass, which will mean that perhaps there will be enough for some coast-to-coast and intercontinental travel. High-speed rail means not just passenger, but also freight traffic. High-speed electric freight trains will have to replace long-distance trucking if we don't want to use large quantities of oil. Finally, most transportation that takes within a city region will need to use electric rail -- with some use of electric buses, small electric trucks, and small electric cars.