The plans would require the city’s so-called black cars to meet fuel efficiency standards of 9.4 liters per 100 kilometers (25 miles per gallon) in 2009 and 7.8 l/100 km (30 mpg) in 2010. Unveiling the new requirements, Mayor Michael Bloomberg said the levels of fuel efficiency required were only achievable using hybrid technology, which mostly involves cars running on a combination of gasoline and battery power.

The city announced last May that its signature yellow taxis would all be running on hybrid engines by 2012. “Between yellow taxis and black cars, more than 23,000 Taxi and Limousine Commission-regulated cars will be required to be more efficient,” Bloomberg said in a statement Wednesday. Bloomberg last year unveiled an ambitious programme to cut the city’s greenhouse gas emissions by 30 percent before 2030 alongside plans to increase access to parks, reclaim unused industrial land and reduce water pollution.

The initiative that received the most attention was a congestion charge for drivers entering Manhattan, aimed at reducing car use in the city as well as improving air quality. The proposal is still under consideration.