It's also possible that people will opt for the easiest, most obvious solution
Recipe for fully-renewable transportation sector
1. Require all vehicles to be flexible fuel equipped, AND
2. Require 30% ethanol to be blended with all current gasoline sold, AND,
3. Gradually reduce the amount of gasoline in the blend to zero, AND,
4. Sell cars that weigh 70 percent less with heavy tax on heavy vehicles, OR,
5. Reduce the number of cars on the roads by 70 percent, OR,
6. Some combination of the above.
--couldn't figure out how to fit the XOR and NOT logical operators in there :-P