For a while now I have been curious about the relative energy demands of different modes of transportation, especially bicycling and walking. Most people would agree that as a modern society we have lost touch with the environment in many ways. Food production is probably one of the most looked at areas in which this has happened but energy demands of our lifestyle are no less important.
For some context watch this video. Imagine if you had to do this every time you wanted to turn on a light. If that isn’t bad enough, imagine if you had to do this for your car’s headlights. You aren’t even moving yet and the energy demands are beyond what is humanly possible. Industrialization and reliance on fossil fuels has made us completely blind to the energy demands we make in everyday life. These are the types of orders of magnitude I have been curious about.
So I decided to do a little research and I was able to find some data on this subject. A human walking around 3 miles per hour on a level surface uses around 5 kcal/minute(1) and a bicyclist riding at ~10 miles per hour on level surface uses around 8 kcal/minute(2). These values mostly vary with speed of travel and slope. Next, I then converted MPG for an average US car and a hybrid-electric bus into BTU/mile/passenger and got the graph below.
These are obviously very rough numbers but it is easy to see the expected trend. A half full bus (29 people) uses less than half as much energy per rider as that of an average car while a packed bus uses 1/8th of the energy per rider. The real dramatic differences though are in bicycle and walking energy use. Walking a mile is over 10 times more efficient while bicycling is almost 25 times more efficient. Even if cars become twice as efficient (54 MPG) bicycling would still be over 12 times a efficient. Next assuming a 20-minute round trip (total of 40 minutes) and given average speed of that mode I then calculated the energy use of a trip by mode. This is reasonable because it accounts for the land uses patterns associated with each mode.
The first thing you should notice is that the relationship between this graph and the last graph is not linear. By accounting for land use patterns I’m able to “weigh” modes by the realistic distance they travel. Very few auto trips are 1 mile for example while most pedestrian trips are in this range. I have a hard time with orders of magnitude so look at the final graph.
This graph shows the number of trips by mode that can be made using the same amount of energy as a single car trip. I don’t know about you but this blows me away. Transit is a significant improvement but is no where near bicycling and walking. This is why dense walkable and bikeable cities are absolutely essential for attaining sustainability. This is just one more example of why our transportation and climate change problems are really in fact land use problems. The profound issues of sprawl and low density development are manifested most significantly in our transportation system. Transit acts as an enabler for a sustainable built environment by removing the necessity of the car and creating densities were bicycling and walking are easy and attractive.
(1) ”Human Energy Expenditure” by R. Passmore
(2)”Influence of age, sex and body weight on the energy expenditure of bicycle riding” by William Adams