The XR-3 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 XR-3 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.