Really?
Internal combustion engines could be more efficient than they are today, but at the problem is, that increased power efficiency leads to higher pollution. Fuels are now formulated to so that the unburned portions are primarily CO2 and H2O out the tailpipe, but the catalytic converter is doing much of this. Modern engines operate somewhere around 15:1, maybe 17:1, air/fuel ration for gas engines. 100% efficiency would be more like 25:1.
Problem is, pollution. The EPA standards are driving lower efficiency and cafe standards are driving fuel efficiency.
It isn't fuel taxes driving . In European nations, people just drive cars with smaller engines and drive far less, unless they are the ~10% or better.
Increased fuel taxes would just increase the costs associated with transportation. Push then high enough, and people will start going electric, but at the expense of making far less people capable of affording personal transportation.