Saturday, February 5, 2011

Number-crunching my holiday road trip, Part II

I wrote in December about choosing transportation options for my winter road trip across contry and tallying the carbon footprint of my trip.  I’m fairly confident that driving resulted in significantly lower emissions than flying would have, and we had an enormously good time sightseeing along the way, visiting friends and family, and enjoying the singular experience of being on the road.

We drove 361 more miles than estimated, but we also improved our fuel economy on the second leg of our trip. We went from 21.9 miles / gallon from St Louis to Las Vegas to 27.5 miles / gallon from Las Vegas to St Louis via Denver.  Together, these two countervailing effects resulted in only slightly higher emissions and costs than expected.

Table 1: Estimated vs. actual stats of our road trip


kg CO2 Emissions

One dimension in which driving is worse than flying is safety.  I haven’t done a careful analysis myself, but a quick search (the sources vary in dubiousness) reveals estimates of the fatality rate per passenger mile on commercial airlines as either about the same as driving, or up to 160 times higher.

Table 2: Airline vs. passenger car safety
Deaths / billion km



NTSB - air

NTSB - car

The final bits of data I collected about energy usage on our trip were readings of our electricity meter when we left and when we returned.  We unplugged everything in the house except the refrigerator, and set the water heater to its lowest level and the thermostat to 61 degrees.  Over the course of 23 days, these basic appliances used 76.5 kWh of electricity, about 28% of the rate during the previous month when were were at home.  According to the EPA calculator for our zip code, our normal usage from September to December was 30% of the average for our area of 900 kWh per month.

The EPA website also provides a cool tool to find out the composition of fuel sources used by local power companies by zip code.  Dishearteningly, my power company Ameren Missouri gets 83% of its power from coal, compared with the national average of 50%.  Our dirtier energy mix results in 38% more CO2 emissions per unit of electricity: 0.83 kg CO2/kWh in Missouri vs. 0.60 kg CO2/kWh nationwide.

Using these numbers, our empty house still generated 64 kg of CO2 emissions while we were gone.  But we saved 162 kg of CO2 compared to our normal usage by not turning the heat up to a comfortable level, not turning on the lights, etc., which ends up being 13% of the emissions used from all that driving during our road trip.  Thus, the amount of energy we saved by staying with friends and family instead of in our own home is still vastly outweighed by the energy needed to transport us across the country.  

Table 3: Household electricity use

Empty house for 23 days
Average normal usage for 23 days
kg CO2

Although it feels exhilarating and carefree, the hard truth is that travel exacts tremendous costs on the environment.  Yet working and living in our society often compels us to do so.  There is no direct way we can compensate the people and ecosystems that are harmed by our travels, but the least we can do is learn as much as we can about the people and places we visit – and perhaps, to learn something about travel itself.  Being nerdy by nature, I've really enjoyed crunching my road trip data.  It's one of my ways to get the most out of traveling, so that all those carbon emissions can contribute to some enduring and shareable insights.  I have a feeling that I’ll be benefiting from the experiences and encounters from this trip for a long time to come.

1 comment:

Lynn said...

Like it very much. I did similar things. keep going.