As New York City works aggressively to reduce its carbon footprint and cut exhaust emissions, it has encouraged large fleets to switch to hybrids. From utility ConEd to the fleets of yellow cabs, more and more hybrids are showing up on city streets.

The latest large fleet to go greener is the New York Police Department, which will add 200 Ford Fusion Hybrid sedans and Ford Escape Hybrid crossovers to its fleet this year alone. The new vehicles will double the department's fleet of hybrids to roughly 400.

Ford Escape Hybrid used as NYPD Traffic Enforcement vehicle, by Flickr user futurehwyguy

Ford Escape Hybrid used as NYPD Traffic Enforcement vehicle, by Flickr user futurehwyguy

NYPD Nissan Altima Hybrid

NYPD Nissan Altima Hybrid

NYPD Altima Hybrid

NYPD Altima Hybrid

The NYPD runs a large number of Ford Crown Victoria full-size sedans, one of Ford's most popular fleet vehicles for both police forces and taxis since Chevrolet ended production of its rear-wheel-drive Caprice a decade ago.

But the V-8 engine in Crown Vics only returns 8 to 12 miles per gallon in mixed city use, with correspondingly high emissions. The ability of full hybrids to switch off their engines when stopped, and run short distances solely on electric power, makes them perfect for urban duty.

Last year, New York's Finest purchased 40 Nissan Altima Hybrids to be used on patrol duty, adding them to a fleet of Toyota Prius traffic patrol cars already in use by the NYPD. A department spokesman said the force's experience with those cars had been "positive."

The two Ford models, since they're built in North America, will likely be bought in higher volume. The 2010 Fusion Hybrid has been a sales success, contributing to a 73-percent rise in Ford's hybrid sales last year.

Police forces have watched from the sidelines while hybrid vehicles have been brutally tested by use as taxis. Several cities other than NYC have already brought hybrids into police fleets, but taxis in two-shift operation put on more miles and see a wider range of road conditions.

They're also likely to be run far longer than patrol cars, which are usually retired at or before 100,000 miles. And any worries about hybrid battery life have been largely laid to rest by early Escape Hybrids that have logged 300,000 miles or more in taxi duty.

Since police forces customarily use sedans, some may wonder why the NYPD is buying Escape Hybrids as well.

Well, rather than using blue or black Crown Vics with low-level trim and wide wheels--easily distinguished on the street--as "unmarked cars," Big Apple cops travel incognito in cars made up to look exactly like yellow cabs, with "Off Duty" signs always on. No one looks twice.

[The New York Times; photo by Samuel Smith from NYCPDcars.50webs.com; photo by Flickr user futurehwyguy]