SAN FRANCISCO - JANUARY 13: San Francisco Mayor Gavin Newsom walks by a display of hybrid vehicles after speaking at a press conference January 13, 2009 at San Francisco International Airport in San Francisco, California. Newsom launched the first in the nation "Green Rental Car" incentive program that offers people a $15 rebate when they rent a hybrid rental car from participating car rental companies at San Francisco International Airport. (Photo by Justin Sullivan/Getty Images)