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Energy Consumption: Bikes v Cars

Bicycling requires 35 kcal/mi. Cars require 1,860 kcal/mi. [Both of those figures are from Marcia Lowe of the World Watch Institute.] Someone here suggested it takes 10 kcal of energy to produce 1 kcal of food. [This is inflated. I remember hearing it takes just under 5 kcal of energy to grow 1 kcal of vegetarian food, sorry I don't have the reference in my possession. Of course, a vegetarian diet is a whole other argument we can get into :) .] Yet another person mentioned there is ~25% efficiency in converting eaten food to useful work. [Note: that's kcal eaten to joules of work; I think Ms Lowe's calculation above is different, referring to kcal eaten to go a mile.] The average diet is about 2,000 kcal/day.

Now for the math.

WORST CASE SCENARIO [using 10 times figure and 25% energy conversion]: 35 kcal/mi ---------- = 140 kcal's of food need to be eaten to bike one mile .25 140 kcal/mi * 10 = 1,400 kcal to grow food to bike 1 mi. 1,860 kcal/mi 1 - ------------- = .25 = Bikes are 25% more efficient 1,400 kcal/mi
BEST CASE SCENARIO: 140 kcal/mi * 5 = 700 kcal to grow food to bike 1 mi. 700 kcal/mi 1 - ------------- = .62 = Bikes are 62% more efficient. 1,860 kcal/mi
Either way you look at it, bikes are more efficient. Now, factor in that both the cyclist and auto driver are going to eat about 2,000 kcal anyway. To go a mile, I'd only have to eat between 2% and 7% more food, if I eat anymore at all.

This page was written by Daniel Convissor as a posting to ba.transportation on 3 July 1994

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Last updated: 7 April 1999