DAY 81_COMPARISON OF MODES OF TRANSPORTATION

3 November 2010

While earlier I looked at how the energy efficiency of driving a car compares to bike commuting, it is interesting to look at all forms of transportation and their efficiency.

We all hear about how much fuel it takes to fly, but is it really that bad compared to driving a truck/SUV or a regular car?  A Boeing 747 travels at 560 miles per hour and uses 3,200 US gallons of fuel per hour.  This is 5.7 gallons per mile, or 0.18 miles per gallon. 
(Tennekes, Henk. The Simple Science of Flight: From Insects to Jumbo Jets, MIT Press, 2009 http://mitpress.mit.edu/books/chapters/0262513137chap1.pdf)
Converting into gallons per mile allows us to then compare the 'passanger gallons per mile', which is a more fair comparison for transport modes that carry more than one person.  A 747 can seat up to 400 people, I used 350 in my comparison. 

A fully loaded subcompact car with 40 miles per gallon (good gas mileage) gets 0.025 gallons per mile (inverse of mpg).  With four people in the car it gets 0.006 gallons per passenger mile, however, it is more rare that people are driving with 4 people, with only two the gallons per passenger mile comes in at 0.012.  The plane with 350 people gets 0.016 gallons per passenger mile.  Pretty close.  So it depends on how many people your family is trucking out to Florida, but if you are comparing just driving vs flying, flying is actually a more efficient use of energy. 

As for buses, according to this article http://www.coloradodot.info/programs/commuterchoices/documents/trandir_transit.pdf a typical Transit Bus is 40' and can hold 42 passengers.  Miles per gallon for a conventional diesel bus is 5.1 mpg and 9.3 for a hybrid electric bus  ("Performance and Fuel Economy Comparitive Analysis of Conventional, Hybrid, and Fuel Cell Heavy-Duty Transit Buses" By V. Dawood and A. Emadi, Grainger Power Electron. & Motor Drives Lab., Illinois Inst. of Technol., Chicago, IL, USA ).  With around 40 passengers the conventional bus gets a gallons per passenger mile of 0.0049, and 0.0026 for a hybrid bus.  So the conventional bus is
5.1 times more energy efficient than driving your car alone, and the hybrid bus is 9.6 times more efficient.

As for those people driving personal light pickup trucks and SUVs, these vehicles are over twice as inefficient than ANOTHER OTHER MODE OF TRANSPORTATION OUT THERE  gallons/passenger mile count is 0.055, 2.2 times worse than a subcompact car and 11.2 times less energy efficient than riding on a conventional bus. 

As for biking and walking, they have no competition.  As mentioned in my previous post, biking (calculating human calorie energy expended) is equivalent to 759,493.7 miles per gallon and walking (burning 100 calories an hour) is equivalent to 314,782.17 miles per gallon.  Biking is 19,230.8 times more efficient than driving your subcompact car and walking is 7,886.4 times more efficient.  Walking burns about 60 more calories per hour than biking making it less 'energy efficinet', but as my roommate pointed out looking at these numbers, when it comes to your own energy, suddenly energy expenditure looks like a good thing.  After all, its renewable :) Eat a sandwich. 

The following graphs show the sequence of information translated from the 'Transportation Energy Data Book' put out by the US Department of Energy, Issue 29).