America’s police aren’t just fighting crime these days, some are helping in the fight for independence from foreign oil. And they’re saving a few bucks in the process.

With budgets getting tighter every year, many departments across the nation are converting their cars to run on propane fuel, which is typically much cheaper than gasoline and, as an added bonus, domestically-sourced. About 85 percent of the propane sold in the United States is locally produced, and nearly all of it comes from North America.

Big cities like Phoenix and Raleigh have already added the alt-fuel cruisers to their fleets, and smaller municipalities are joining them. With help from a clean energy grant from the North Carolina Solar Center, the Iredell County Sherriff’s Office in Statesville recently had 13 of its Ford Crown Victoria Interceptors turned into bi-fuel vehicles that can run on either propane or gasoline. Propane isn’t renewable, but it creates less pollution and carbon dioxide than gasoline, qualifying it as a clean fuel.

The conversions were done with help from Alliance AutoGas, a consortium of 30 businesses that sell and install the equipment needed to make the modifications and provide the propane supply. Alliance spokesperson Steve Whaley tells FoxNews.com that a conversion costs about $5,800 dollars, but that his company is training the Iredell County mechanics to do it themselves, eliminating labor costs and bringing the price down to just $4,000.

It’s a lot of money up front, but in North Carolina, propane is about $1 cheaper per gallon equivalent than gasoline. With the kind of mileage police cars put on each year a conversion quickly pays for itself. As with most propane sellers, Alliance will set up a refueling station for free, so the department only pays for the fuel and the clean-burning nature of propane cuts down on maintenance costs, as well.

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Iredell County Police Captain Mike Phillips says his officers think the performance of the cars is as good, if not better than the standard Crown Vics. While they retain the ability to run on gasoline for emergencies, the cars have a range of 290 miles per tank of propane. The only visible modification is the cylindrical tank that holds the fuel, which is installed on the upper shelf of the trunk, so there’s still plenty of room for gear.

The cars have been so well-received by the force and the city that Phillips says the department just ordered 16 more, which it’s paying for in part with seized drug money. Eventually, the county would like to convert at least a third of its 150 car fleet.

Whaley adds that when they build them, other municipal departments often come along for the ride. In Greenville, SC, which has 100 propane-powered police cars, 20 different agencies now use a variety of vehicles that run on the fuel, and Alliance has installed 3 refueling stations across the city.

There is some bad news, at least for criminals who learned their trade watching Hollywood movies. The in-car tanks are constructed of carbon steel and can withstand a direct hit from a variety of bullet calibers, including a .357 Magnum. Even if a puncture occurs the, gas usually vents and the tank doesn’t explode.

Besides, the crooks would have to open the trunk to get a clear shot. If they’ve gotten that far they should probably just steal the car instead of blowing it up. It’d save them some money during the getaway.

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