Buying A New Car Is Greener Than Driving An Old One...Really

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Old cars recycled to plant trees [Photo: Flickr user lonely radio]

Old cars recycled to plant trees [Photo: Flickr user lonely radio]

You've probably heard it at some point: A friend claims his older vehicle is far greener than the new car with much higher fuel economy you just bought

That's because, he says, the old car didn't require all the energy and natural resources your car consumed as it was built.

But is that older car really greener?

The short answer: No.

The longer answer is also 'no', but it may help educate your friend on why that beloved 20-year-old rattletrap isn't as green as he likes to think.

The environmental cost of manufacturing

It's easy to see why many people think that running an old car would be greener than regularly buying new ones.

2001 Honda Insight

2001 Honda Insight

Building a new car is an energy- and resource-intensive process. You need to mine ore out of the ground and oil from the earth or sea, turn them into the raw materials for vehicle parts, turn those supplies into actual components, and then assemble the resulting parts into a car.

At the end of it all, you've got a rolling ton or more of metal, plastic, glass, and rubber that didn't exist before. That carries an environmental cost long before the car turns a wheel.

But it's here that we return to a 2000 study by M.A. Weiss et al., entitled On The Road In 2020: A life-cycle analysis of new automobile technologies.

The study reveals that fully 75 percent of a car's lifetime carbon emissions stem from the fuel it burns, not its production. A further 19 percent of that is production and transportation of the fuel, leaving just six percent for the car's manufacture.

These figures vary--a more recent Volkswagen study suggests that with vehicle efficiency rising steadily, 68 percent of the car's lifetime emissions came from driving it, while the manufacturing process accounts for a higher 22 percent.

Some of this discrepancy is down to the VW in question, an ultra high-efficiency model available in Europe. The less energy a car consumes through its lifetime, though, the less that fuel use contributes to its lifetime emissions.

Volkswagen Golf TDI BlueMotion

Volkswagen Golf TDI BlueMotion

The numbers

We can actually work out the relative merits of running an old car and a newer, more efficient one. The numbers show why it becomes better to buy a new car rather than keep an older one running.

Let's say you drive an older car that does 30 mpg, and you drive 15,000 miles per year. The newer car does 40 mpg--as many modern compacts can, or will shortly.

During those 15,000 miles, your old car will use 500 gallons of gas. The newer car: 375 gallons.

That 30 mpg is also about 290 grams per mile of CO2; 40 mpg works out as 217 g/mi. Over the course of the year, the old car will emit 4.35 tons of CO2, the newer car 3.25 tons.

But if you've been running the older car for 10 years, it has emitted over 43 tons of CO2 before the new car has even been built. That number will keep on going up, so bear that in mind if you drive something made in the 1990s or earlier.

MORE: Five Big Myths About Green Cars And Gas Mileage, Debunked

According to The Guardian, citing How Bad Are Bananas? The Carbon Footprint of Everything by Mike Berners-Lee, a minicar has a production footprint of around 6 tons of CO2 equivalent. A larger car--a Ford Fusion--is about 17 tons before it hits the road.

If we assume our 30- and 40-mpg compacts both account for about 12 tons of CO2 during production, it's easy to work out just how long it would take for a new car to offset its production.

In its first year, the new car is responsible for 15.25 tons of CO2 (12 for production, 3.25 during use). That's about 3.5 years of using the old car at 30 mpg, in terms of carbon emissions.

Of course, the older car's production also adds to its tally--and it's less likely that older vehicle included as many recycled materials, or were built as efficiently as the newer car.

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