actually the solution comes (in the short term anyway) in engineering rather than the fuels.
the best way to solve this is to improve the other systems of the vehicle.
conventional car breaks rub on the disc slightly all the time - waste
they convert Ke into heat - waste
batterys need charging - lost motive power
wheel bearings have quite a high friction - waste
all the bits of trim and panel gaps cause aero losses - waste
the way to see us for the next 50 years at least is to start producing lighter vehicles, cars have got way too heavy. a lot of this is from the extras added on to the vehicle, when you next get in your car take a look at all the extra crap thats added on to your vehicle and question if you really need it?
(for the uk guys, oz or SA is a bit different here) do you really need air con?
what about power steering? if its less than a ton then i bet you dont.
what about your heated electric adjust seats?
also something to remember is a lighter car is a faster car that turns better, i for one will take that over air con anyday.
for comparison a mk1 fiesta is about 850kg and a new one is close to the weight of my bmw.
the aerodynamics of some of the new cars out atm is shocking, much could be improved there (and i know some of it is new pedestrian safety stuff but come on a ton of steel is going to kill you any way, looking left and right wont.) flat fronts need smoothing, grills need reducing and slats to air air flow. the under body of some new cars could improve lots. simple things but free efficiency.
electrical systems dont need an alternator anymore. regenerative breaking and a new solar covering is capable of doing the job (technically) free for us now.
this is a ramble, iv been up all night, ill sort it out later.