In the United States, the days before and after the annual Thanksgiving holiday represent busiest days for travel in the U.S. each year. If you care about the environment, what do you suppose is the mode of travel that will consume the least amount of energy on average and will have the smallest carbon footprint for how far you might travel to be with your friends and family this year?
The answer may surprise you! We've visualized data showing the trends for the average energy intensity, or rather, the average energy consumed per passenger mile, for several different modes of passenger transportation in the U.S. from 1975 through 2016 in the interactive chart below. If you're accessing this article on a site that republishes our RSS news feed, please click through to our site to access it there.
In the chart, "Light Truck" refers to any two-axle, four wheel truck, which would include anything from pickup trucks to SUVs. "Air" refers to commercial air travel, while "Intercity Rail" in the U.S. means train travel via Amtrak.
Probably the most remarkable thing is how air travel has become less energy intensive per passenger mile than both transit buses (after 1996) and cars (after 2004). The second most remarkable thing we find is how transit buses have become worse over time.
We should note however that the values in the chart represent the average for each mode of passenger transportation. Individual vehicles within each mode have a wide amount of energy intensity variation, where your carbon footprint for travel will depend on it. For example, there's a big difference in fuel efficiency between jets that began flying 25 years ago and are still in service and newer versions that have rolled off their assembly lines more recently. The same is true for all the other modes of transportation.
Environmentally speaking, the average BTUs per passenger mile for each mode is directly proportional to the amount of carbon emissions it produces, where each 1 million BTUs consumed produces the equivalent of 53 kilograms of emitted carbon dioxide. If you're traveling, the greenest thing you can do is choose the least energy intensive mode of transportation that can get you to where you need to be within the time you have available to travel.
If you're traveling to your Thanksgiving destination today, you have our sympathy!
Davis, Stacy C. and Boundy, Robert G. Transportation Energy Data Book. Edition 37.2. Table 2.14: Energy Intensities of Highway Passenger Modes, 1970–2016. Table 2.15: Energy Intensities of Nonhighway Passenger Modes, 1970-2016. Oak Ridge National Laboratory. [PDF Document]. August 2019.