The Porsche 911 Carrera Cabriolet on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The Nissan Leaf electric vehicle on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The 1952 Mercedes 300SL race car on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The 2013 Ford C-Max Energi plug-in hybrid electric car on display at North American International Auto Show, Detroit, Michigan, USA, North America

The 2012 Toyota Prius plug-in hybrid on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The Toyota Prius plug-in hybrid electric car on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The 2012 Toyota Prius plug-in hybrid on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The Smart For-us concept electric pickup truck on display at the North American International Auto Show, Detroit, Michigan, USA, North America

The BMW i8 plug-in hybrid concept car on display at the North American International Auto Show, Detroit, Michigan, USA

The Volkswagen e-Bugster concept plug-in electric vehicle on display at the North American International Auto Show, Detroit, Michigan, USA, North America

Two Chevrolet electric cars on display at the North American International Auto Show; the yellow EN-V pod-like car is a concept; the red Volt is in production, Detroit, Michigan, USA, North America

The 2013 Chevrolet Spark on display at the North American International Auto Show, Detroit, Michigan, USA, North America