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is fuel economy the right metric?

July 31, 2007

As I recently reported, I’m getting great fuel economy with my New Beetle TDI. Since starting my commute between Waterloo and Stratford late last year I’ve managed to improve my fuel economy from 8.0L/100km down to 6.5L/100km through driving style changes, and then down to 4.9L/100km by switching to a more fuel-efficient vehicle. It certainly seems like I’m heading in the right direction, but I’m not entirely convinced that’s correct. My fuel economy numbers are great right now – but is fuel economy the right metric to use?

In a world where everyone drives, fuel economy is a good starter metric. If we can get people to start tracking their fuel economy, chances are they will start looking for ways to improve. That’s good from a dip-your-toe-in-the-water point of view, but looking towards true sustainability, we have to look at a different metric: total fuel use.

I now use about 5L/day in fuel to get to work and back. Assuming I work 5 days a week for 50 weeks a year, that means I use 1250L of fuel per year. Now look at a hypothetical example of someone driving a Hummer to and from work. Assume they’re getting an abysmal 20L/100km, and driving 20km round-trip 5 days a week for 50 weeks a year. Their fuel use is actually only 4L/day, or 1000L of fuel per year. All else being equal, who is driving greener?

Yes, I realize that instead of driving a Hummer they could downsize to.. well, just about anything would be downsizing… and reduce their fuel use even more. That isn’t the point. The point is that regardless of their fuel economy, they are using less fuel annually than I am in my biodiesel-burning Beetle. Consequently, their carbon footprint is actually smaller than mine. Like it or not, using less total fuel trumps better fuel economy.

There are complications to using total fuel use as a comparitive metric, such as how you’d count carpooling or taking mass transit, but these issues are no worse than if you are using simple fuel economy numbers. Short of using a full carbon emissions grading system, you’re not going to be able to track absolutely all the fuel used on your behalf. Nor should you try at this point – the idea is to shift your viewpoint from how much fuel you are using per unit distance to how much fuel you are using per year. By doing so, the amount of driving that you do will be included in the measurement, which is an important part of how much fuel you use in total.

I’d like to be able to reduce my daily fuel requirements, period. The only way to do that is to move closer to work, telecommute, or find a job that is closer to home. Deciding and implementing that change will be a lot trickier than the purchase of a fuel-efficient vehicle. In the meantime, the best I can do is to use a biodiesel blend to reduce my transportation-based net carbon emissions.

One Comment leave one →
  1. Jerry permalink
    July 31, 2007 8:50 pm

    I’d like to be able to reduce my daily fuel requirements, period. The only way to do that is to move closer to work, telecommute, or find a job that is closer to home.

    Which highlights the big decision about environmental awareness, the choice that everybody has to make; at some point, you have to decide when being environmentally aware becomes too much of an inconvenience to your life. There’s no such thing as zero impact; best any of us can hope for is to achieve a balance that we’re comfortable with.


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