May
13
2009

Hey, it's Walk/Bike to Work Day tomorrow. And in honor of that, here's a little math problem to keep you occupied, courtesy of Guesstimation: Solving the World's Problems on the Back of a Cocktail Napkin by Lawrence Weinstein and John Adam.

"What are the relative costs of fuel (per kilometer or per mile) of New York City bicycle rickshaws (human-pedaled taxis) and of automobiles?"

Bicycle rickshaw: What does it take to fuel this?
Bicycle rickshaw: What does it take to fuel this?Courtesy ARoberts

You might need a few hints.

  1. How far does a bicycle rickshaw travel in one day?
  2. What does it cost to fuel (i.e. feed) the bicyclist?
  3. How far does a car travel on a gallon of gasoline?

What'd you get? Post your answer as a comment. Once a few folks post answers, I'll post the one from the book, as well as the "work."

Your rating: None Average: 4 (2 votes)

Your Comments, Thoughts, Questions, Ideas

Liza's picture
Liza says:

OK, so how would you even start to figure it out?

Here's a cool calculator that will show you how far your car can travel on a gallon of gas. I put in a bunch of different makes/models of cars, of different ages. For the sake of easy math, I'm going to say, on average, a car can go 20 miles on a gallon of gas. (Yes, I'm sure your car does better. And this is, after all, a guesstimate.)

According to Twin Cities gas prices, a gallon of gasoline today will run you about $2.20.

So $2.20/gal divided by 20 mpg = $0.11/mile (or $0.07/km).

When I carry passengers on my bike, I can go a maximum speed of maybe 15 miles an hour, but I'm much slower on hills, maybe 7 miles an hour, and I probably average somewhere around 11 miles an hour. But I'm carrying two kids, not two adults, so I should pick a number at the low end of that range. And, of course, a pedicab is not always moving. So for the sake of easy math, I'll just say an average of maybe 5 miles per hour. Assume an 8-hour working day, and that gives you 5 mph x 8 hrs/day, for a total of 40 miles per day.

Calculating fuel for the cyclist is the tricky bit. The CIA's World Factbook estimates the US per capita GDP at $48,000. That works out to $132/day. And this 2006 Forbes article says Americans spend about 13% of their income on food. So we spend maybe $17/day on food.

$17.00/day divided by 40 miles/day = $0.42/mi or $0.27/km.

The car uses more energy per mile, but gasoline is a cheaper fuel than food. However, the fuel costs for the car depend on the distance traveled. If you double the distance traveled by car, you double the fuel cost. With a pedicab, the fuel cost is the same, per day, no matter how far you go.

And, of course, you're probably eating today whether or not you're pedaling a rickshaw. So get out there and ride! Don't let that fuel go to waste!

posted on Thu, 05/14/2009 - 2:38pm
Anonymous's picture
Anonymous says:

Guess what? This article that I just read has motivated me to hop on my neglected bike and pedal to the metal, as they say. I am sure that my workplace will enjoy and/or appreciate all of the work that I will be doing, and I might get some positive reinforcment with my fellow collegues! However, I regret to inform you that I was a little concerned with the content portion of this article, as I believe more information is necessary to have a more substantial impact of the denizens of society. I was, however, plesantly surprised at the amount of money per mile a cyclist pays. Thank you, and have a nice day.

posted on Wed, 08/18/2010 - 11:19am

Post new comment

The content of this field is kept private and will not be shown publicly.
  • Allowed HTML tags: <a> <h3> <h4> <em> <i> <strong> <b> <span> <ul> <ol> <li> <blockquote> <object> <embed> <param> <sub> <sup>
  • Lines and paragraphs break automatically.
  • You may embed videos from the following providers vimeo, youtube. Just add the video URL to your textarea in the place where you would like the video to appear, i.e. http://www.youtube.com/watch?v=pw0jmvdh.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Images can be added to this post.

More information about formatting options