A new study authored by University of Wisconsin-Madison engineers introduces public audiences to the carbon dioxide (CO2) emission impact of different modes of transportation through a simple online calculator.
To drive home the point, however, that calculator also translates pounds of CO2 into one of the nation’s favorite foods: the cheeseburger.
The researchers, civil and environmental engineering PhD student Erin Bulson and postdoctoral researcher Wissam Kontar and their colleagues, published their study in the May 2024 issue of the Nature journal NPJ Sustainable Mobility and Transport.
The two say one of the challenges of educating the public about various transportation modes’ environmental impact is that it can be difficult to envision how much CO2 an individual trip might pump out. Adding to that complexity is the fact that it can be even more difficult for people to comprehend what a pound of CO2 emissions really means.
“We thought carbon emissions might not necessarily be intuitive to the public,” Bulson says. “We wanted to use a different way to communicate this information, so we tested it out with cheeseburgers, which is unique and happens to be a culturally appropriate fit for Wisconsin.”
The calculator’s approach is simple: Enter a trip’s distance and it shows the estimated carbon emissions for cars (gas, electric and hybrid), a bus ride, bicycling (regular and electric), and walking. Then, the calculator converts all of those pounds of CO2 into a cheeseburger equivalent (about 4 pounds of CO2 per burger). The research showed promising results: 46% of study participants reported having a better understanding of CO2 emissions after a three-month period of using the calculator. Additionally, their own travel mode changes typically resulted in fewer emissions.
A 10-mile trip generates about 9 pounds of CO2 emissions for a traditional gasoline car, 5 for an electric car, 6 for a hybrid car, and nearly 6 for the bus. In cheeseburger equivalents, that works out to approximately 2 burgers for the gas car, 1.24 for the electric, 1.44 for the hybrid, and 1.42 for the bus. Taking an electric bike produces an estimated .15 pounds of CO2—or a miniscule .04 cheeseburgers. Walking and using a normal bicycle did not produce CO2 emissions.
Postdoctoral researcher Wissam Kontar and PhD student Erin Bulson, during their study, created a calculator that converts carbon emissions to the equivalents produced in making a cheeseburger. Credit: Joel Hallberg.
It’s not the first time burgers have made it big in research. For example, the Big Mac Index, created by The Economist in 1986, uses the Big Mac to illustrate differences in purchasing power parity across countries. Similarly, researchers have considered the carbon impact of a cheeseburger—1.9 kilograms, or roughly 4.2 pounds, of CO2 per burger—while studying how displaying carbon emissions affects customer decisions in restaurants.
Bulson and Kontar used the Greenhouse Gases Regulated Emissions and Energy Use in Technologies (GREET) model created by Argonne National Laboratory to assess the life cycles of the different transportation modes to determine their emissions.
The researchers conducted a study with 49 participants in Madison, Wisconsin, who each used the calculator for at least 20 trips. Before the study began, the team conducted a survey that collected basic demographic data, information about travel habits, and an assessment of participants’ environmental awareness. Throughout the study, participants kept track of their intended transportation mode for each trip and whether checking its CO2 emissions with the calculator changed their transportation plans.
Almost half the study’s participants reported changing transportation modes at least once. Sixteen percent of the total trips (155 of 978) involved a shift, with the most frequent being gasoline car to bus, bus to walking, and gasoline car to walking. Overall, participants recorded about 544 pounds less CO2 emissions due to travel mode changes. That’s about 130 cheeseburgers.
“Overall, the net result from these changes was a positive environmental implication, which means a reduction in emissions,” Kontar says. “From a socio-economic perspective, we saw that income, trip distance and a person’s environmental awareness were the best predictors of whether someone would change transportation modes.”
Bulson and Kontar hope their study sets the foundation for further research, with larger and more geographically diverse surveys. Ultimately, they hope the calculator, or a similar tool, can be integrated into navigation apps to display planned trips’ carbon emissions for users to consider, just as we do now when weighing the estimated travel time and distance of one route against another.
“If you use Google Maps, you might see that your home is 3 miles away and it’s a 20-minute trip, and with traffic maybe it’s 30 minutes,” Kontar says. “You get familiar with that because you keep using it over and over again. It’s data, and people trust data. It’s an easy way to gain trust and build understanding about emissions from real life experiences.”
Bulson and Kontar are also considering expanding the comparison food beyond cheeseburgers—for example, comparing a trip’s emissions to the carbon impact of an apple or to popular regional foods.
One thing is clear: Based on feedback, the study’s participants liked the cheeseburger references in the calculator. Bulson says the study’s final survey included several responses that indicated thinking of their trips in terms of burgers helped participants grasp how emissions vary from trip to trip and travel mode to mode.
“Maybe at first glance it doesn’t sound terribly scientific, but anything that encourages people to use this is a good thing,” Bulson says. “At the end of the day, the crux of what we’re looking at is how we can get more people engaged with these tools to better understand and reduce carbon emissions.”
Bulson is a student under Keith and Jane Nosbusch Associate Professor of Civil and Environmental Engineering Andrea Hicks. Civil and Environmental Engineering Professor Soyoung Ahn also collaborated on the research. Kontar studied under Ahn and Hicks before graduating in 2022.
Featured image caption: UW-Madison civil and environmental engineering postdoctoral researcher Wissam Kontar and PhD student Erin Bulson have published a study about the carbon emissions of various modes of travel. Credit: Joel Hallberg.