Mayor Michael Bloomberg said the city would start adding 300 new hybrid vehicles to its taxi fleet every month, with three automakers guaranteeing to supply the cars. Ten percent of New York’s 13,150-vehicle taxi fleet already consists of hybrid cars, and the city is on schedule to meet its goal of converting the entire fleet to hybrid technology by 2012. Bloomberg said the Nissan Motor Co. has agreed to sell 200 hybrid Altimas to taxi operators every month, and Ford and Chevrolet will each supply 50 hybrid vehicles. Hybrid taxis get 25 to 30 miles per gallon in the city, twice the mileage of non-hybrid taxis. The chairman of the city’s Taxi and Limousine Commission said that switching to hybrids will save the average taxi driver about $6,500 a year in fuel costs. Bloomberg, whose hybrid taxi project is just one of 127 green initiatives he is proposing, has touted the reduction in air pollution and greenhouse gas emissions.