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Energy Blog: Transportation Emissions Under the Microscope

Energy Blog: Transportation Emissions Under the Microscope

Two recent reports explain why reducing the carbon footprint of driving around may be a major challenge.
There was good news on the climate in a recent report from the Rhodium Group, an independent energy research group in New York City. According to preliminary data on 2023 greenhouse gas emissions, the United States matched a 2.4 percent growth in its GDP with a 1.9 percent drop in carbon emissions. That followed two years where GDP growth led to emissions increases.

While emissions from the power sector decreased by 8 percent and those from buildings (both residential and commercial) decreased by 40 percent, those attributed to transportation increased in 2023. In fact, the power sector, which once produced the largest amount of carbon emissions due in large part to coal-fired generating stations, now ranks below both the transportation and industrial sectors.

Transportation emissions are up by around 14 percent since the pandemic year of 2020, the Rhodium Group found.

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“Transportation sector emissions increased by 1.6% in 2023 relative to 2022, mostly driven by a continued rebound in jet fuel consumption after the pandemic. Available seat miles, a measure of how many seats are available on commercial flights, have rebounded above 2019 levels comparing the first three quarters of each year and appear to be on track to set a new record,” the group noted in its January 10, 2023, report, Preliminary US Greenhouse Gas Emissions Estimates for 2023. “Through September 2023, road traffic volumes were also up 2.2% over 2022 levels, contributing to an increase in gasoline consumption.”

According to data from the U.S. Department of Transportation, the 3,221,813 million vehicle miles traveled in the 12 months ending in September 2023 were the third highest level on record, surpassed only by the levels in 2018 and 2019.

In spite of the gains made by electric vehicles, the number of vehicle miles traveled corresponds closely with fuel consumption and therefore emissions.

Long-distance driving

One factor buoying the number of vehicle miles traveled is the small number of drivers who cover a disproportionate number of miles. According to a report from the Seattle-based non-profit organization Coltura, when American drivers are categorized by the amount of fuel consumed, the top 10 percent of drivers—a cohort Coltura terms “gasoline superusers”—burn 35 percent of the fuel consumed in the United States.

To put the figures in a more global context, the report noted, “The 21 million U.S. gasoline superusers make up just 0.24 percent of the world’s population, but they use 10.4 percent of the world’s gasoline—nearly as much as all of China.”

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The report makes use of data that had heretofore not been combined to look at individual fuel consumption. The data includes odometer readings collected on individual cars and trucks, information linking demographic and vehicle data in 110 million households, and cell phone and other GPS data that tracks individual trips taken by 210 million drivers. The data was combined to provide a way to link drivers, cars, and miles driven.

It turns out that the top 10 percent of drivers consume 1,278 gallons of gas per year on average. That’s four times as much as the median drivers, and these superusers consume as much gasoline as the bottom 70 percent of drivers combined. Compared to non-superusers, who average 24 miles of driving every day, superusers drive 116 miles a day during the week and 97 miles on the weekend. They are overrepresented among blue-collar workers and people who live in rural areas. They are also overrepresented in the states of North Dakota, South Dakota, and Wyoming, where these gasoline superusers make up more than 15 percent of motorists and consume more than half the gasoline burned in those states.

“Superusers spend on average $530 a month on gasoline, versus non-superusers at $110 a month,” the report noted. “Across all income levels, Superusers spend on average 10.2 percent of household income on gasoline, versus non-Superusers at 3.5 percent. The difference is particularly striking at lower income levels. Among about 1.7 million Superusers making less than $25,000 per year, the share of household income spent on gasoline averages 41.3 percent.”

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Given the burden of fuel costs that arise from so much driving, it would be natural to imagine that gasoline superusers would be looking for more efficient vehicles, but that seems not to be the case. According to the data from Coltura, more than 61 percent of gasoline superusers drive an SUV or pickup, and they get worse fuel economy than any other cohort.

Coltura wants to use this data to identify which drivers to target for converting to electric vehicles. “An average Superuser switching to an EV achieves a net CO2 reduction of roughly five times as much as the average non-Superuser switching (11.3 metric tons per year, versus a non-Superuser at 2.3 metric tons per year),” the report noted. A complete switch to EVs would reduce U.S. carbon emissions by more than the emissions from the aviation industry.

That potential may be difficult to reach, as the long-distance rural highway driving that is common for gasoline superusers is considered a tough market for EVs. The drivers who would most benefit from switching away from gasoline vehicles may well be the last to do so.

Jeffrey Winters is editor in chief of Mechanical Engineering magazine.

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