SAN FRANCISCO, CA - FEBRUARY 08: A passenger gets into a Toyota Prius hybrid taxi cab in front of a Union Square hotel on February 8, 2012 in San Francisco, California. San Francisco city officials ... more 
SAN FRANCISCO, CA - FEBRUARY 08: A passenger gets into a Toyota Prius hybrid taxi cab in front of a Union Square hotel on February 8, 2012 in San Francisco, California. San Francisco city officials announced today that 92 percent of San Francisco's taxi fleet is comprised of hybrid or CNG vehicles making San Francisco the greenest cab city in the nation. (Photo by Justin Sullivan/Getty Images) less 
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Getty Images | Photo By Justin Sullivan / Getty Images
Wed, Feb 8, 2012 5:04 PM EST