KEY CONCEPTS
• A study evaluating emissions generated by sedans, SUVs and pickup trucks throughout the continental U.S. was done down to the smallest regional level known as a county.
• While higher emissions are generated in the production of BEVs compared to ICEVs, the break-even time for when emissions produced by BEVs is equal to emissions produced by ICEVs is between 1.2-1.6 years depending upon the vehicle type.
• Conversion to BEVs from ICEVs in the U.S. will reduce emissions no matter how rapidly the U.S. electric grid decarbonizes in the future. 

The focus of studies showing how electric vehicles reduce emission has been on analyzing light-duty sedans and station wagons. Overall, light-duty vehicles account for 58% of transportation emissions in the U.S. according to the Environmental Protection Agency (EPA). But sales of new sedans in the U.S. in 2020 represent only 31% of total light-duty vehicle sales. The largest market share of new car sales in 2020 was accounted for by trucks at 56%. This category includes truck SUVs, pickup trucks and vans. The majority of sales in this vehicle type were truck SUVs (39%) with pickup trucks accounting for 14% and vans the remainder.

Maxwell Woody, research specialist at the University of Michigan’s Center for Sustainable Systems in Ann Arbor, Mich., says, “We recognized that with trucks and SUVs becoming a much larger segment in the light-duty vehicle category, a life cycle assessment (LCA) study needed to be conducted to determine how emissions of this vehicle type will change in moving from an internal combustion engine vehicle (ICEV) to a hybrid electric vehicle (HEV) and eventually to a battery electric vehicle (BEV) over the lifetime of each vehicle type. This covers all emissions attributed from the manufacturing of these vehicles (including sourcing of the raw materials used in their production) until the end of their operating life.”

Woody and colleagues from the University of Michigan and Ford Motor Co. conducted such a study that involved an evaluation of emissions generated by sedans, SUVs and pickup trucks throughout the continental U.S. during the lifetime of these vehicles. Woody says, “We utilized figures prepared by the U.S. National Highway Traffic Safety Administration for the average distance that each vehicle type covered during its operating lifetime. Sedans are estimated to operate for 290,000 kilometers, while SUVs and pickup trucks operate for 320,000 kilometers.”

This analysis was done down to the smallest regional level in the U.S., which is a county. There are 3,108 counties present in the continental U.S.

The researchers factored in such variables as temperature, electric grid emissions in a specific county attributed to the source of power generation and driving patterns. Woody says, “Temperature is a more significant factor for BEVs than the other vehicle types because batteries prefer to operate at ambient temperatures between 16 C and 24 C. Battery performance suffers above and below this temperature range. We used a linear approach to show that battery performance will decrease proportionally as the temperature deviates from the desired range.”

Electric grid emissions are another parameter that need to be taken into consideration. Woody says, “We utilized a model developed by the National Renewable Energy Laboratory (NREL) known as Cambium that projects power generation emissions by region.”

Driving patterns need to be accounted for because electric vehicles display better performance and lower emissions in urban environments compared to ICEVs. In contrast, rural locations are of more benefit for ICEVs due to higher fuel economy figures and concern about the driving range of BEVs between charges.

Woody says, “For each U.S. county, we determined the ratio of city to highway driving as the way to estimate the percentage of driving in urban versus rural environments.”

The researchers used two models to obtain the information required to do the study. Woody says, “The Autonomie model simulated energy consumption for the three vehicle types using the three powertrain options. Data on materials, manufacturing and end-of-life-emissions were obtained using the GREET 2021 model.”

Different performance categories also were examined by the researchers. In the base case, BEVs with a range of 480 kilometers between charges were used while other battery ranges that included 640 kilometers and 320 kilometers also were analyzed. Woody says, “Emissions for batteries increased with range due to the greater weight, which means that more intensive manufacturing is required. Our analysis shows that a battery with a range of 480 kilometer has a 16%-17% lower emissions rate than one with a 640 kilometer range.”

With battery manufacturing being such an important parameter in judging the LCA for BEVs, the researchers also determined the break-even time, which represents when emissions for BEVs will be equal to those of ICEVs and HEVs. Woody says, “Higher emissions are generated in the production of BEVs compared to ICEVs. This is due to the processes used in the manufacture of batteries. It is estimated that double the greenhouse gas (GHG) emissions are produced in the manufacture of BEVs compared to ICEVs. When in use, ICEVs display higher emission levels than BEVs. The break-even time for BEVs is 1.2-1.3 years for sedans, 1.4-1.6 years for SUVs and 1.3 years for pickup trucks.”

The researchers found that for the three vehicle types studied, BEVs have a 64% lower cradle-to-grave life cycle emissions in sedans than ICEVs in the base case. HEVs have a 28% lower cradle-to-grave life cycle emissions than ICEVs in the base case. The carbon dioxide emissions benefit for BEVs over ICEVs is 45 metric tons of carbon dioxide for sedans, 56 metric tons for SUVs and 74 metric tons for pickup trucks.

Figure 1 shows the life cycle GHG emissions for all three vehicle types across the continental U.S. Woody says, “Our data shows a significant variation on emissions for each vehicle type based on location and timing for when a BEV is charged. The reason is due to the impact of ambient temperature on vehicle efficiency, the variability of the electric grid and the type of power generation used in each specific region of the U.S. But clearly, BEV displays lower emissions meaning that the move to electrification of vehicles will lead to an overall reduction in carbon dioxide emissions.”


Figure 1. GHG emissions for the three vehicle types (sedans, SUVs and pickup trucks) organized by powertrain (ICEV, HEV and BEV) is shown in the continental U.S. by county. Figure courtesy of the University of Michigan.

The researchers determined that BEVs outperform ICEVs in 98%-99% of all U.S. counties and outperform HEVs in 95%-96% of all U.S. counties from an emissions standpoint. Woody says, “We estimate that conversion to BEVs will reduce emissions no matter how rapidly the U.S. electric grid decarbonizes in the future.”

Future work will involve evaluating how emissions will change by 2030 when BEVs are expected to represent 50% of all new vehicle sales in the U.S. Additional information can be found in a recent study¹ or by contacting Greg Keoleian, professor at the University of Michigan School for Environment and Sustainability and director of the Center for Sustainable Systems. Keoleian is a co-author of the study and can be reached at gregak@umich.edu.

REFERENCE
1. Woody, M., Vaishnav, P., Keoleian, G., Kleine, R., Kim, H., Anderson, J. and Wallington, T. (2022), “The role of pickup truck electrification in the decarbonization of light-duty vehicles,” Environmental Research Letters, 17 (3), 034031.