Basically, it has been estimated that there is only enough land to produce sufficient quantities of ethanol to displace at most 30 percent of our current consumption of gasoline. The remaining 70 percent reduction has to come from improved fuel economy, primarily via weight reduction but also from more efficient engines & transmissions.

Setting an initial goal of 30-to-70 percent ethanol-gasoline mix for flex-fuelled vehicles would be a good way to start. Single-seat vehicles would probably achieve the weight reduction needed to completely eliminate gasoline from the mix, but all vehicles on the road would have to reduce their weight by an average of 70 percent. Another approach might be a 35 percent weight reduction and a conversion to hybrid electric powerplants with a 35 percent improved efficiency, to achieve the 70 percent reduction in consumption. However, hybrid cars are more expensive, whereas single-seat cars are proportionally less expensive compared to full-sized cars, without any exotic materials or high-tech engines.

Overall, I think full renewability in the transportation sector is readily achievable. It simply requires people to make that choice, to do that.