The toxic emissions saved is from a formula developed by
Patrick Goebel of Global Cycling Org (Velonet).  It is a
measure of the amount of pollutants that would have been
emitted if an "average" automobile had been driven instead
of the bicycle.  The pollutants included are: total
organic gases (TOG), carbon monoxide (CO) and nitric
oxides (NO).  These pollutants are generated when an
engine is "cold started" (number of trips = N) and while
running (number of miles = D).  Averaging for traveling at
25 mph and 55 mph gives the following formula for
ES=Emissions Saved:

ES = TOG + CO + NO
   = [(4.69 + 45.43 + 2.72) * N] + [(.66 + 4.575 + .72) * D]
   = (52.84 * N) + (5.955 * D)

Finally, ES in grams is divided by 454 to give the number of
pounds of pollutants saved.


The calories burned is from the "bike_power" program by
Ken Roberts of Columbia University and refined by Mark Grennan
of Oklahoma Office of State Finance.
The calculation is based on many variables including the following:
G	grade of the hill (vertical_rise/distance)
HEAD	headwind [meters/second],7 multiplier crosswind
SPEED	MPH
TF	temperature in F (affects air density)
WM	weight of bicycle (lb)
WC	weight of cyclist (lb)
AC	frontal area (m^2): 0.4925155 for upright position,
	0.4297982 crouch, 0.3080527 racing, 0.1844627 in pack
R	rolling friction: 0.012 for mountain bike tires,
	0.004 racing slick, 0.0051 27x1.25 tires
E=0.249	efficiency of human in cycling
T=0.95	transmission efficiency of bicycle drivetrain
A1=0.0	linear coefficient of air resistance
C_a=0.9	air resistance coefficient
BM_rate=1.4	basal metabolism rate [Watts/kg body weight]


Finally, the pounds of fat burned is calculated from the calories
by 7000 calories per pound of fat.

shell script to calculate car emissions
shell script to calculate calories burned