New York's yellow taxis will go hybrid in five years, in an effort to cut air pollution and tackle climate change, Mayor Michael Bloomberg has said.
The fuel-efficient cars will save taxi drivers about $10,000 per year
Hybrids run on petrol and electricity, therefore emitting less exhaust.
The new vehicles are to be phased in immediately, replacing the current fleet which numbers about 13,000.
"The benefits are going to be felt by generations of New Yorkers. Going hybrid will shrink the city's carbon footprint," Mr Bloomberg said.
The environmentally-friendly models also achieve greater mileage to the gallon.
Currently the city's taxis get about 14 miles per gallon on average, while the new fleet would provide fuel efficiency of about 30 miles per gallon.
"Implementing tougher standards for the more than 13,000 taxis in this city will provide the same clean air benefits as removing 32,000 privately owned cars from our streets," Mr Bloomberg said.
Hybrid vehicles are more costly, but the City Council said the increase in fuel efficiency will save taxi drivers more than $10,000 (£5,000) every year.
The move is part of the mayor's ambitious plan for a 30% reduction in the city's greenhouse gas emissions by 2030.