The XR3 Hybrid is a super-fuel-efficient two-passenger plug-in hybrid that achieves 125 mpg on diesel power alone, 225 mpg on combined diesel and electric power, and performance like a conventional automobile. The design of the XR3 Hybrid focuses on existing technologies and a vehicle personality that makes conserving energy a fun driving experience. It showcases the design ideas explored in Robert Q. Riley's book, Alternative Cars in the 21st Century.

At just 1480 pounds, this high-performance design combines fast acceleration, a maximum speed of 80 mph, and fuel economy of 125- to over 200-mpg.

Its clam-shell canopy and three-wheel platform boldly differentiates the XR3 from conventional passenger cars. The vehicle's hybrid power system, diesel engine, and low curb weight are the main ingredients of its super-high fuel economy and excellent performance. Acceleration equal to that of a conventional car and a maximum speed of 80 mph make the XR3 Hybrid equally at home on freeways and surface streets.

Plans enable people with common building skills to build a duplicate of the XR3 Hybrid prototype or convert their own car into a significantly more fuel-efficient vehicle. Readers will understand the factors that influence fuel economy, and learn how to make any car achieve greater fuel economy. The XR3 Hybrid gives enthusiasts and experimenters the opportunity to significantly reduce their transportation expenses and have fun doing it. On a broader level, the vehicle is a highly visible example of the kinds of vehicles that could help reduce personal mobility energy.