Legislating all new cars to be flexible-fuel equipped will allow consumers to switch fuels without buying a new vehicle.

The amount of energy needed to propel a motor vehicle is described by the equation:

KE = 0.5 * m * v^2

where,
KE = kinetic energy
m = vehicle mass
v = vehcle speed

All highway speeds being equal only lighter vehicles will burn less fuel, regardless of vehicle type. Better aerodynamics and larger diameter wheels will help too.

My motivation? I don't own a car, but I buy goods and services whose prices are affected by the transportation sector. Perpetually increasing oil prices would put a serious dent in my quality of life. When most people hear about renewable energy, they think solar or wind energy. But it's really the transportation sector that's key, and liquid fuels are essential. Therefore efforts need to be specific ---> engines, fuels, and production methods. Solar, wind, hydroelectric & nuclear power simply don't help the transportation sector.