Monday, August 11, 2008

Transportation Efficiency

(NOTE: The masthead of my blog reads, "... the most efficient form of human transportation ever devised - BICYCLES!" Am I prepared to back that up? Should I elaborate from time to time?)

Late last month, I wrote a little about the Car of the Future, a PBS Nova episode exploring future transportation.

Among other things, the program pointed out that a typical internal-combustion vehicle is extremely inefficient, in converting fuel into transportation energy. (Since much of the power is scrubbed away "between the engine and the rear wheels," and also because most of the remaining power is devoted to moving the vehicle itself, rather than its occupants or payload.)

One of my cycling brothers, bob t, replied, "... I was wondering if any studies had been done regarding the efficiency of a bicycle." He searched and found some info, "Pedal power probe shows bicycles waste little energy." (Click HERE to link.) Engineers at Johns Hopkins University determined that a bicycle is at least 81% efficient, in using energy for transportation. Amazing, particularly when you consider that the standard "safety bicycle" design hasn't changed significantly in almost 130 years. (If anything, it's become more efficient as bicycle weight has dropped significantly in that time.)

Of course, it's difficult to make an objective comparison in transportation efficiency between a car, a bus, a train, a bike rider, etc. How do you measure the amount of energy expended?

A guy - a biology professor named Vance Tucker at Duke University - tried to do just that in a study he conducted a few years back. (He had been studying the amount of energy expended by various bird species while flying, and got the notion of expanding that study.)

He came up with these numbers:
Automobile (1 occupant) - 1,860
Transit Bus - 920
Transit Rail - 885
Walking - 100
Bicycling - 35


Tucker's conclusion: "Statistically, the most efficient animal known in the entire universe is a human being on a bicycle."

If somebody has some conflicting or more recent data... BRING IT! I'd feel awful if I were perpetuating lies or myths.


Scott said...

That puts things into perspective, doesn't it? With roughly 30,000 calories in a gallon of gas, even a 100mpg scooter uses about 300 cal/mi. So even "efficient" vehicles suffer by an order of magnitude.

I'd guess that large gliding birds (buzzards, eagles, albatrosses) might have bicycles beat for efficiency, but I have nothing to back that up.

Scott said...

Huh. Sprocket diameter can make a significant difference in efficiency. It's better to use the large ring and a larger (Lower) gear than the middle ring and a smaller (Higher) gear with the same ratio.

I learned something new.

Clancy said...

Numbers like that are very provoking. I can tell you when you are that efficient, you notice little differences in your bike. Maybe a brake out of adjustment or a low tire. It feels like I am dragging a parachute behind me sometimes.

Anonymous said...

Scott: As I understand it (based on similar previous studies) the gliding birds are more efficient than a bicycle when gliding, and much less efficient when gaining altitude by flapping. Their overall efficiency will vary drastically depending on the availability of thermal updrafts. Val

NoIdleHands said...

Bike Nazi,
Prof. Tucker did expand on his work as noted here

good news/bad news

Bicyclists are still more efficient than the omnipresent automobile, but not as efficient as freight ships or freight trains (and likely passenger trains by extension).


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