I think the folks at the Rocky Mountain Institute may be a little optimistic with their modeling. But here it is straight from the Rocky Mountain Institute.
Excerpts from RMI.org -
The HyperCar FAQ
Modeling by RMI suggests that full-sized Hypercar® vehicles should be able to get 90 miles per U.S. gallon of gasoline or equivalent (2.6 L/100 km) in the near term and 200 mpg (1.2 L/100 km) in the long term.
How could Hypercar® vehicles attain such dramatically improved fuel economy?
A car's fuel economy can be improved by reducing any or all of the following:
· aerodynamic drag
· rolling resistance (due mainly to tires)
· drivesystem inefficiencies (the drivesystem includes the engine and all mechanical components
connecting the engine to the wheels, such as the transmission and differential)
· energy lost during braking
· accessory loads (lights, audio system, climate control, instrumentation, etc.)
Minimizing these losses piecemeal is good, but redesigning the entire car for maximum overall
efficiency—taking an integrated, "whole-system" approach—is much better.
Ultralight Construction
... All told, it should be possible to make Hypercar®
vehicles that are 50-65 percent lighter than conventional cars of the same size.
Aerodynamics and Rolling Resistance
Today's cars are already fairly sleek, but aerodynamic drag can be further cut by 40-50 percent or more through cab-forward design, a smooth underbody, a tapered rear end, minimized body seams, and aerodynamically designed air intakes, suspension, and wheel wells.
FWIW,
Tim