Monday, April 25, 2011

Bike transportation - not so efficient after all?

I've smugly declared that bicycles are "the most efficient form of human transportation ever devised." And I'm rarely, if ever, challenged on that assertion.

One reader observed that if you consider the cost of calories for that amazing "hybrid bicycle engine" - you know, what you spend at the grocery store - it might not be so cheap after all. But a person has to eat whether he drives a car or rides a bike, so it's very hard to measure... and I continue to maintain that all things considered, a bicycle is considerably cheaper than any alternative.

But... maybe not?

I found an amazingly comprehensive report called Bicycle Energy by David S. Lawyer. He has some interesting and detailed observations.

On the surface, indeed a bicycle seems more efficient by many-fold, over a fossil fuel-powered automobile.

But Mr. Lawyer points out that for every food-calorie burned in riding, it might take 10 calories to grow, distribute, and cook that food. Nit-picky?

How about this one... Do you want to factor in the life expectancy of the vehicle? He observes that while an automobile might last a 200,000 mile lifetime, a bicycle lifetime is 525 miles. (525 miles? What the??? Per month, maybe? But consider the millions of bikes that will never be anything more than the occasional recreation toy. Many of them probably do only last 525 miles - spread over 10 years.) If you factor that in, one car might take the driver (and passengers) many hundreds of times more than one bicycle, over the lifetime of the vehicle. So maybe per mile, the energy to manufacture a car is less than for a bicycle... all bikes considered.

He's got all sorts of stuff - rolling resistance, aerodynamic drag, inclines and descents, small car vs. big car, etc. You guys with your slide rules and scientific graphing calculators might really enjoy it. (My head started aching, so I just kinda skimmed over a lot of it. And if you're asking, "What's a slide rule?" you were born too late! It's kinda halfway in between that graphing calculator and the abacus.)

Let's ride!

1 comment:

Scott said...

I wrote a paper in college asserting that the world is flat. I laid out several compelling arguments and equations as proof, and I got an A on the project. The fact that I proved it don't make it so.

One glaring omission from his thesis was the energy cost of fuel. While he went to great lengths to explain how one calorie of food requires 10 calories of fuel, he failed to calculate how many calories of fuel are consumed by drilling, refining, and transporting that fuel to your car.

I'd also point out that his 525 mile lifetime was an apples-to-oranges argument since it lumped all cars and all bikes together as transportation devices. Most bikes are recreational and NOT primary transportation machines, and I would exclude these just like I would motorcycles and motorhomes. I would estimate the useful life of a bike receiving the same level of maintenance as a car, to be several hundred thousand miles. You can ride a (real, non-department store) bike until the frame dies by replacing things as they fail just as a car will need batteries, tires, windshields, and clutches over the normal span of its life.