An Experiment in Transportation Efficiency

Stephen K. Boss, PhD, PG 

Director, Environmental Dynamics Program
Co-Director, Sustainability Curricula

I had the opportunity to attend the annual conference and exposition of the Association for the Advancement of Sustainability in Higher Education in Nashville, Tennessee on October 6-10, 2013, with Todd Knobbe, a Geosciences graduate student.

Participation in the AASHE conference presented an opportunity to conduct an experiment in transportation efficiency.  Given that the meeting was within reasonable driving distance from Fayetteville, Knobbe and I decided to track carbon intensity and cost of travel to the conference by private vehicle and compare it to the carbon intensity and cost of travel by air.  The objective was to assess the carbon dioxide emissions and cost effectiveness of automobile travel versus air travel to this particular meeting.

Note that we focus exclusively on the carbon emissions and direct transportation costs, discounting entirely an evaluation of wear and tear on the vehicle (which we assume is minimal compared to the anticipated lifetime of the vehicle) or other considerations, such as travel time and relative safety of air travel versus automobile travel.

We drove my 2010 Toyota Prius and, to assist in minimizing travel footprint while in Nashville, transported two bicycles to ride while at the conference to gain additional savings on fuel (and thus, carbon footprint) and money (saving costs for fuel and downtown parking).  We parked the car at no cost at the hotel and biked approximately 7 miles daily (round trip) to the downtown conference center.

The total carbon footprint for their travel was estimated from their vehicle mileage and performance characteristics.  The round trip from Fayetteville to Nashville totaled 1085 miles.  My Prius consumed a total of 20.7 gallons of regular unleaded gasoline for average fuel efficiency of 52.5 miles per gallon.  The U.S. Energy Information Administration reports that most unleaded gasoline in the U.S. now contains about 10% ethanol and combustion of 1 gallon of this fuel releases 17.68 pounds (8.02 kilograms) of CO2.  Thus, the total CO2 emissions from this road trip were:

20.7 gallons consumed x 8.02 kilograms/gallon = 166.01 kg of CO2.

Of course, since two people were transported, we can divide this total by two to determine a per person transportation footprint of 83.00 kilograms of CO2.  The total fuel cost for this trip was $76.98, or $36.99 per person.

For the two of us, total carbon emissions for air travel would have been 844.74 kg of CO2 compared to our actual 166.01 kg of CO2 for vehicular travel and the total cost would have been $1,360 for air travel compared to $76.98 for vehicular travel.

We compare the emissions and cost above to emissions and cost had we traveled by air to this conference.  Since there are no direct, non-stop flights from Fayetteville to Nashville, we examine the emissions for the most likely air route we would have used: Northwest Arkansas Regional Airport (XNA) to Nashville, TN (BNA) via the Dallas-Fort Worth International Airport (DFW).  The International Civil Aviation Organization maintains an online calculator to determine carbon dioxide emissions for air travel using standard protocols.  Using this calculator, the CO2 footprint for these routes was estimated to be:

  • XNA-DFW (round trip):   166.09 kg of CO2 per person
  • DFW-BNA (roundtrip):    256.28 kg of CO2 per person
  • TOTAL:                               422.37 kg of CO2 per person

Cost of this round-trip flight would have been $680 per person.

For the two of us, total carbon emissions for air travel would have been 844.74 kg of CO2 compared to our actual 166.01 kg of CO2 for vehicular travel and the total cost would have been $1,360 for air travel compared to $76.98 for vehicular travel.  Here we report only the cost of air travel, omitting emissions and costs related to airport transfers in Nashville and travel by private vehicle to and from XNA for departure and return.

Thus, for this trip, the carbon footprint of travel by Prius was 5 times less than the carbon footprint of travel by air.  Cost savings were even more dramatic.  Air travel was 18 times more expensive than vehicular travel!  This experiment demonstrates that for travel within an 8-10 hour driving radius, vehicular travel yields a much smaller emissions footprint than air travel, and is vastly more cost effective.  It would be interesting to compare the cost of vehicular travel over air travel as a means of managing emissions for trips shorter than 600 miles one-way.

Feel free to comment or ask questions below!

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