Wednesday, September 19, 2012

The Cost of Fuel

I saw this image on Reddit today and thought, hey, that's not right. All methods of transportation require fuel. For the bike it just happens that the fuel is food rather than gasoline or diesel. As it turns out, gas stations tend to ubiquitously offer two things, fuel for automobiles and snacks for humans. So, in actuality, the price not only completely inaccurate, we can actually calculate approximately what that price should be.

The price of the gasoline is set per gallon here in the US. In order to compare to food we need to compare in terms of a common quantity, a quantity that combines the energy density and efficiency of the engine. The quantity that really cuts to the chase combining all of these factors implicitly is the distance that you can travel. Specifically, we seek to compare the distance you can travel per dollar, which is actually how you should compare most energy sources, cost divided by some benefit measure.

A car can typically travel around 30 miles on one gallon of gasoline. The price of gas around where I live is on the order of 4 USD per gallon. This means that it costs 13.3 cents to travel a mile in your car.

A simple Google search tells us that a typical bicycle rider burns around 50 kcals per mile. At a gas station, with their premium on convenience, you can expect to spend something like 2 USD on a glorified bottle of sugar water which contains a total of 125 kcals of energy. This means that it cost you 80 cents to travel a mile on your bike.

Therefore, if you are purchasing fuel from a gas station and have the choice between travel by car or travel by bicycle, and care only about the cost of fuel to do so, it is much cheaper, six times cheaper, to purchase your fuel in the form of gasoline and drive your automobile around than to purchase food and ride your bicycle around.

But that's not all. The URL on the gas station sign tells me that this station is in Austria. They are on the Euro and the current cost of gasoline there is something like 1.4 Euro per liter, so I suppose the price at this station is 1.46 Euro for a liter of diesel. Another Google search tells us our 2 USD sugar water would cost 1.50 Euro assuming gas station snack foods cost the same as they do in the US. This corresponds to 37.5 euro cents to travel a km on bike to 11.4 euro cents to travel a km in a car, a ratio of 3.28, smaller but still favors travel by automobile. This means that the price on the sign should say something like 4.787 Euro.