So it looks like someone in Kansas is building diesel-electric hybrids. Just not really from scratch.

Johnathan Goodwin converts vehicles, new and old, to diesel-electric hybrids. His clients include Governator Arnold Schwarzenegger and Neil Young.

Young happens to hang out on one of the train forums I frequent (he's the minority owner of Lionel) and they asked him to elaborate. Some people took him to task for ruining a classic by removing its original engine. He said the car was a beater when he first acquired it. He also said he does expect to get 100 miles per gallon out of it, and its range will be longer than one can safely drive nonstop. He'll plug the car in at night, and for a short trip or commute, the car wouldn't have to use the biodiesel at all.

The conversions aren't cheap--Young sold some cars from his collection to finance the project. It typically costs $40,000 to convert a car. But it's nice to see that the super-rich can convert their big cars to pollute less than my Honda Civic does.

It makes me wonder, though. If Young's 1959 Lincoln Continental will get 100 miles to the gallon, what kind of mileage would a converted Honda Civic get?

Young also said that if cars using this kind of setup were mass-produced, the cost would be comparable to a Cadillac Escalade or Lincoln Navigator. That's 2-3x what I paid for my Civic.

Let's do the math. I drive about 400 miles a week. At $3 per gallon, I'm spending $34.29 a week on gas. According to what Young said, I could probably do all of my driving purely on plug-in power, but let's assume the worst-case scenario and say I'd burn 4 gallons of biodiesel per week. Call it $12.

So I can expect to spend $1782.86 per year in my Civic. If I were driving one of these biodiesel-electric hybrids, I'd spend $624.

That's a lot of money, but I'd have to drive that hybrid 17 years to save more than I save by driving my Civic. That's 353,600 miles. A Civic can last that long if you're careful with it, but will one of these hybrids? I guess it depends how good the rest of the car is.

Under the best-case scenario where I don't use any biodiesel at all, the time drops to a more reasonable 11.22 years or 228,800 miles. That's still a lot longer than most people are willing to drive the same car, but I could see myself driving one car for 12 years.

If gas hits $4 per gallon, then it takes 13 years and 269,231 miles for it to even out under the worst-case scenario, and 8 years and 175,000 miles under the best-case scenario.

Of course, Neil Young's point is that not everyone wants to drive a Honda Civic, so the comparison isn't entirely fair. If you want to drive something big that would get 15 miles to the gallon running if it were burning gasoline, the comparison is more fair.

At $3 per gallon, things even out at the 5.66 year/117,647 mile mark under the worst-case scenario, if you put a price premium of $20,000 on the hybrid version. Under the best of circumstances, it evens out at 4.8 years/100,000 miles. That's not entirely unreasonable.

At $4 per gallon, it looks even better: 4.24 years/88,235 miles worst-case, 3.606 years/75,000 miles best-case.

Since most people like to keep their cars about four years, this is looking practical. And if these hybrids have a higher resale value than conventional cars, which is highly likely--ever price a used Toyota Prius?--it looks a lot more practical.

The CNN article says people are beating down Goodwin's door to partner with him. I can see why, and I'm glad.

As for me, I've been trying to do the math and make things work, but no matter how I juggle it, I'd have to keep a gas-electric hybrid or a diesel car about 10 years before it would pay for itself compared to a conventional Honda Civic or Toyota Corolla. I'm perfectly willing to keep a car 10 years but I'm not sure I want to pay the premium up front. I did the math back in 2003 and ended up buying a Civic. At the time I made the decision based on $1.75/gallon for gas. Even if gas hits $4/gallon next year, it looks like the time isn't right yet for me to change course.