When people talk about alternative fuels, propane isn't usually the first topic that comes up. This is because they’ve probably never driven in a propane-powered vehicle, and for the past few decades have been bombarded with all kinds of talk about ethanol (E85), hydrogen and flux capacitors being the saviors of the human race.

So you may be surprised to hear that propane is actually the third most commonly used motor vehicle fuel, ahead of all of those, compressed natural gas (CNG), and eye of newt. According to the U.S. Department of Energy there are even more places to buy propane than E85. Maybe the reason it doesn't come up too often, then, is because it's not really all that alternative.

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A quick primer. Propane is a byproduct of both petroleum refining and the processing of natural gas, so it's a fossil fuel and a non-renewable resource. However, more than 85 percent of the propane sold in the United States comes from U.S. soil, literally, and pretty much all of the rest of it is imported from Canada and Mexico, which makes it appealing to energy security types. Although it is widely used as a heating fuel, much of what is recovered is burned off as waste during oil refining, as anyone who has driven down the New Jersey Turnpike at night can attest to.

A gas in its natural form, propane is easily compressed into a liquid, making it less cumbersome to transport and store than CNG or Hydrogen. It’s also very pure and clean-burning, with the added benefit of being non toxic to the environment, which is why you can install a tank of it just about anywhere and use it to barbecue brisket. The combustion process also produces less carbon dioxide than gasoline or diesel.

While it seems like the perfect motor fuel for today’s political environment, early engines using vapor injection systems didn't operate as well as gasoline engines, and couldn't get much of a foothold beyond commercial and government fleet applications where user friendliness is secondary to cost and clean air initiatives. As a result, the public propane refueling infrastructure of about 2,500 stations pales in comparison to the roughly 150,000 gasoline stations in the United States, despite the fact that new liquid injection technology allows a propane vehicle to operate almost identically to a gasoline powered one.

I know this, because I recently spent a day behind the wheel of a Ford F-150 pickup truck that was converted to run on propane by the folks at Roush Performance Products, he same guys you know and love for building 500 horsepower Ford Mustangs, not to mention souped-up F-150s that think they're Mustangs.

• Click here for PHOTOS of the Roush Propane F-150

Visually, the only difference between Roush's truck and a stock F-150 is the big white 59 gallon propane tank in the bed. Most of the modifications take place underhood, and even there it takes a trained eye to pick out the new fuel rail assembly, fuel injectors and fuel lines installed on the 5.4 liter V8.

While there are any number of propane conversion kits available for a variety of vehicles, the Roush product comes with a 3 year/36,000 warranty on modified parts, and preserves Ford's warranty on the rest of the vehicle. Right now it is only available on 2007/2008 model year F-150s, and 2009/2010 F-250s and F-350s, but next year Roush will be adding an Econoline van conversion, reflecting the commercial appeal of the vehicles. You can either purchase a truck on your own and bring it to a dealer for a conversion, or in the case of the newer models, buy a complete vehicle straight from Roush.

I can spend the better part of your afternoon describing how the Roush F-150 drives, but it's easier if I sum it up this way: it drives like an F-150.

The engine has the exact same power and torque as the gasoline version and delivers it the same way. Payload and towing capacity are also unchanged, minus the 200 pound hit you take carrying that tank in the bed (a smaller 25 gallon toroidal tank that fits in the spare tire bay is also available, but range drops from 500 miles to 250.) The only discernible difference from the driver's seat is that when you turn the key the truck takes a couple of seconds to check the pressure in the tank before starting the engine. This is to ensure that it is at proper operational levels for the fuel system, not because it thinks the thing might explode.

The EPA rates the flammability of propane lowest of all alternative fuels and the tanks are stronger than the one in your gasoline or diesel-powered car. Although it is pressurized, the level used is much lower than that for CNG or Hydrogen, around 350 psi compared to 3,600 and 12,000, respectively. Both of which are considered safe, too.

• Click here for our review of the CNG-powered Honda Civic GX

• Click here for our review of the hydrogen-powered Chevrolet Equinox

A gallon of propane contains less energy than gasoline, and Roush says that mileage drops between 1 and 3 mpg. Compared to E85, which has even less energy and cuts fuel economy by 4 to 6 mpg in Ford’s own flex fuel version of the F-150, that's not too bad, but it does bring up the subject of economy and that’s where things get complicated.

The Roush conversion costs about $8,000. There's a $2,500 tax credit available from the federal government on the F-150 and $5,000 for the F-250/350, along with various state and local incentives as well, but a couple of grand is still a pretty hefty outlay if the only payoff is altruism.

Currently, retail pump prices for propane are higher than gasoline, but when it cost $4 a gallon last year, propane was almost a buck cheaper. That's if you're buying the stuff from the local U-Haul or Flying J along with a fill up for your Weber grill. For fleet operators, who can get propane at a volume discount, the price can be as low as $1 a gallon. Toss in a 50 cents per gallon tax credit, which private individuals also qualify for, and your company accountant might actually start to cheer up, until he realizes he'll be filing a lot more tax forms next year.

Depending on how much you plan on driving, even a single vehicle owner can potentially make a deal with their local propane provider for a cut rate price. Jack O’Loughlin of Bay Gas Service on New York’s Long Island said he will even install a 1,000 gallon pumping station on your property for free if you sign a big enough contract for his services.

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So, as is the case with the other fuels from the alternative scene, using propane takes some effort on your part. That's the price you pay to keep your hard-earned money close to home.

At least when you hit the gas - uh, we’ll call it an energy pedal from now on - you feel no pain.

Now if Roush can just figure out how to fit that V8 into a Mustang I may have to schedule another test drive with them.

What do you think of the Roush Propane F-150?

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