Is it possible to build an SUV with the same size and performance characteristics but significantly better fuel economy?

That's what the Union of Concerned Scientists wanted to figure out. The reference vehicle was a Ford Explorer (21 MPG). The UCS designed blueprints for  two models (called the Guardian and the Guardian XSE) to compare against the Explorer.

The Guardian uses a better engine, low rolling resistance tires, improved aerodynamics and a stronger but lighter unibody frame. It achieved a mileage rating of 27.8 MPG. The vehicle cost would be about $600 higher than the Explorer, but would save about $2,500 in fuel over the life of the vehicle.

The Guardian XSE uses an even more efficient engine, low rolling resistance tires, a six speed automatic transmission, and greater use of high strength steel and aluminum to reduce weight. It achieved a mileage rating better than 36 MPG. Initial cost is $2,315 higher than the Explorer but fuel savings amounts to over $4,300.

Various safety features were added to make the vehicles even safer than a conventional design, despite the reduced weight.

Interestingly, the prototypes do not use hybrid technology, but rely on advanced engine designs such as VTEC (used by Honda). One of the drawbacks to rapidly building a very large number of vehicles with a hybrid engine would be availability of the nickel metal hydride batteries, which are already in limited supply. The UCS designs present another option.

UCS's  report was published in September 2003.

UCS is an independent nonprofit alliance of more than 100,000 concerned citizens and scientists. UCS augments rigorous scientific analysis with innovative thinking and committed citizen advocacy to build a cleaner, healthier environment and a safer world.

UCS website