The most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka! (I found it!) but rather, "hmm.... that's funny...." Isaac Asimov

Sunday, August 8, 2010

Still in Service - Why?


My 1985 GMC S15 pickup is still in service. Why? Economics seems reason enough to a penny-pincher like me, but there’s more to it.

The economics are simple. Long since paid for, this truck’s costs are essentially limited to fuel and repairs. There’s no need for more than liability insurance. Repairs don’t amount to much; it’s only driven 3,000 miles per year, and I have a good friend who’s an expert mechanic. Junkyards are full of parts. Payments on a newer truck might be $300 a month or more. If you divide that by the number of times a month I start it up, maybe 15 times, it’s as if the old truck spits out a $20 bill every time I turn the key.

A bigger issue though is the environmental and safety impact of a vehicle. This truck emits about three times the carbon monoxide, nitrogen oxides, and hydrocarbons per mile as a new truck would. But in most parts of the country, the air is cleaner these days. Driven as little as it is, the contributions of this truck to the dwindling air pollution problem seem relatively trivial. The safety issue is more problematic; this truck has no air bags, no anti-lock brakes. Yet, since it’s mostly driven locally and during the daytime in good weather, I estimate my chances of staying alive with it aren’t too much worse than they’d be with a new truck. Neither of these impacts seems to rise to the level of truly important to me.

Evidence is building, however, that there’s an environmental problem that’s far bigger than emission of conventional air pollutants. This is climate change, which is clearly driven by greenhouse gases emitted by human activities. The best reason to keep an old vehicle on the road may well be its fuel-efficiency compared to a newer vehicle, since burning gasoline emits carbon dioxide, the major greenhouse gas.

The energy tally for motor vehicles has two main components; the energy used in producing a new vehicle, and the energy used in driving it.

It takes about 80 gigajoules of energy to produce a light-duty motor vehicle, including mining and producing the metals and other materials, assembly, and end-of-life recycling.[1] This is a vehicle’s “embedded energy.” It translates to approximately 5 metric tons of carbon dioxide emissions. Once on the road, combustion of a gallon of gasoline releases about 8.9 kg carbon dioxide. At 25 miles per gallon, driving 12,000 miles therefore releases over 4 metric tons of carbon dioxide. So, over a ten year lifetime, the carbon dioxide emitted by driving far outweighs that emitted from producing a vehicle. Keeping a vehicle longer improves the ratio of embedded to operating energy still more. For most drivers then, it makes sense from a greenhouse gas perspective to junk an old vehicle in favor of a new one if the new one is significantly more fuel-efficient.

But that’s a problem, because there aren’t more fuel-efficient trucks available in the U.S. market! This truck was designed in the 70s when the nation cared a lot about fuel economy. It is small and simple. It has no power steering, no power brakes, no power windows. It gets 28 mpg on the highway. Amazingly, even if I wanted to, I couldn’t buy a new truck that gets better mileage than this truck. Most new trucks have far worse mpg. So until more fuel-efficient trucks are on the market, or until some truly major repair is needed, I’ll continue to drive the most beat-looking truck in the parking lot. And I’ll continue to enjoy its major side-benefit of, in effect, sliding a $20 bill into my wallet every time I start it up.

[1] Stodolsky, F., A. Vyas, R. Cuenca, and L. Gaines, 1995, Life-Cycle Energy Savings Potential from Aluminum-Intensive Vehicles, Argonne National Laboratory, Argonne, IL 60439

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