Carbonic Math: A Real-world Travel Example

A former boss told me my sensitivity to cognitive dissonance was a drawback in a world defined by same. That may be but when the dissonance gets too loud I like to turn to data. It may not convince you; working with it tends to soothe me.Carbon-dioxide-unit-cell-3D-balls

The lovely image to the right shows CO2 molecules arrayed in a 3D space. Working on my post about lawn reclamation and sustainability prompted me to dig a bit into the numbers behind CO2 emissions. I’m not a scientist or engineer (I work with engineers but washed out of the pre-engineering program I attended in high school) so everything that follows is an educated layman using available numbers and a modicum of common sense.

Our example is a recent business trip from New York to Reston, VA. To keep things easy let’s stipulate that because all but 20 miles was highway driving that we’ll consider it all highway driving.

Item Car 1 Car 2 TOTALS
Miles Driven (R/T NY-Reston, VA  588  588
 MPG (EPA Hwy)    27    33
 Gals Used   21.8   17.8   39.6
 Gas Price/Gal (refuel in DE)  $ 3.65  $ 3.65
Fuel Cost $ 79.49 $ 65.04 $ 144.53
Tolls $ 15.80 $ 15.80 $  31.60
Rental Charges $ 201.25 $ 289.35 $ 490.60
Total Expenditures $296.54 $370.19 $ 666.73
Lbs of CO2/gal 19.643 19.643
 Total lbs CO2  427.781  350.003  777.8

Now, just for giggles, let’s assume that the Metro extension to Reston from DC was working. That would enable us to take Amtrak from NY to Union Station in DC and the metro the rest of the way. The following data come from our friends at, see the citations on their site for the underlying calculations.

Item Group 1 Group 2 TOTALS
Amtrak Distance NY-DC RT (PM) 452 452  904
Distance rail CO2/PM      .42 .     42
Lbs Carbon/passenger 189.84 189.84
# passengers    2    1      3
Lbs Carbon 379.68 189.84 569.52
Ticket Price $ 744 $ 372 $ 1,116
DC-Reston Distance RT 48 48
Passenger Miles (PM) 96 48  144
Commuter rail lbs CO2/PM 0.35 .35
Lbs Carbon 33.6 16.8 50.4
Cost (Max metro fare, one way) $    5 $  5
Commuter Rail Cost R/T all passengers $  20 $  10 $ 30
TOTAL RAIL COST $ 764 $ 382 $1146
TOTAL RAIL CARBON (lbs) 413.3 206.6 619.9

So here’s the conundrum–it’s cheaper to drive–in 2 cars–than to take the train. In fact, even with tolls,  it’s $479 cheaper. And the cars spewed 158 more pounds of carbon into the air. I thought the difference might be greater, so there’s a risk someone would say is that all? I mean, that  was the result of displaying Big Mac calories and people don’t change cognitive styles when products do. Nonetheless, leave aside global warming and you still have to admit that’s not a healthy lungful.

We all know what the fix is. You equalize the costs so that the less harmful method is not disadvantaged vis a vis the more polluting one. There are two words in plain English that say that more clearly: carbon tax. Divide the saved carbon by the difference in price and you get a tax of $3.04 a gallon so that the additional carbon has a price. That raisers the per gallon cost to $6.69. Not crazy by non-US standards but a shocker here at home.

Will we need to have such a tax or see such prices to get people out of cars? I think so. The economists would say behavioral changes require an incentive. For now, most folks balancing a budget or making business travel decisions will choose the overall cheaper alternative. Nobody likes higher taxes but it’s really the only way change will ever happen.

And if we fail to enact such a levy and the impact on the earth gets worse? Well, the economists have a term for that, too: the tragedy of the commons.


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