SAN FRANCISCO – The AAA of Northern California is switching its entire fleet of 400 vehicles to hybrid Toyota Priuses and Ford Escapes. Most of the 250 cars to join the AAA fleet in 2006 will be used by AAA insurance employees, who travel frequently as part of their work. Another 150 hybrid vehicles are set to replace current models over the next two years, according to the organization. The switch made sense after a study showed that the AAA would save money in the long term by replacing its gas-powered cars with fuel-hybrid vehicles. But AAA would have introduced hybrid vehicles in any case because the new fleet is part of AAA’s Greenlight Initiative, a program intended to “promote the development and understanding of new automotive fuels and fuel-related technologies,” the organization reported. The switch will set the organization on the same course as the City of San Francisco and some of San Francisco’s cab companies, which have also introduced hybrid vehicles into their fleets in recent years. The City and County of San Francisco introduced a plan in 1999 to buy clean air vehicles whenever possible, and now San Francisco uses 121 Priuses, four hybrid Chevy Silverado pickup trucks, and two hybrid Ford Escapes on official business.