Decarbonising Light-Duty Vehicles: Achieving U.S. Emission Goals

Street and highway in NYC featuring signs for the George Washington Bridge, with smoke emitting from a car's exhaust pipe.

Key things to know: 

• Transportation accounts for approximately 27% of U.S. greenhouse gas emissions, with light duty vehicles (LDVs) being the largest contributors within this sector.
• The U.S. aims to electrify 50% of new LDVs by 2030 to significantly reduce greenhouse gas emissions, aligning with broader climate goals.
• Challenges in transitioning to electric vehicles (EVs) include the need for increased production of critical battery materials and the decarbonization of the electric grid to maximise environmental benefits.
• Equitable access to EV benefits requires addressing disparities in adoption across states through financial incentives, expanded charging infrastructure, and educational campaigns.

Introduction

Transportation was responsible for around 27% of the greenhouse gas emissions across the U.S. from 2020-21 and was the largest contributing sector. Within the transport sector, light duty vehicles (LDVs) are the largest sub-sector and account for around 50% of these transportation emissions and around 75% of passenger miles alone. The U.S. government has plans to electrify 50% of new LDVs that are sold in the U.S. market by 2030. The main driver behind the initiative to create more electrified vehicles is to reduce economy-wide greenhouse gas emissions from 2005 levels by up to 50% by 2030. 

However, the transition to electric vehicles (EVs) presents its own set of challenges, particularly in terms of the raw materials required for battery production. Studies highlight the need for a significant increase in the production of critical minerals such as lithium, cobalt, and nickel to meet the demand for EV batteries. This surge in demand could strain global supply chains and raise environmental and ethical concerns related to mining practices. Therefore, advancing battery recycling technologies and exploring alternative battery chemistries with lower environmental impacts are crucial steps towards sustainable electrification of the LDV fleet.

It's estimated that electric vehicles (E.V.s) will have similar upfront costs as conventional vehicles by 2030-2035, and leading automotive manufacturers already have many plans in place for the rapid electrification of vehicles over the next decade. While E.V.s will help to reduce greenhouse gas emissions, large-scale adoption of E.V.s could help control pollution levels in cities and improve air quality for people who are living in highly urbanised environments. 

Transitioning to Electric Vehicles: Economic and Environmental Impacts

New fuel economy standards put forward by the Environmental Protection Agency (EPA) in the U.S. could theoretically enable around 67% of new LDV sales to be electric by 2032. There are even some states―such as California―that are pushing for 100% of LDV vehicle sales to be electric by 2035. 

If the U.S. is to take advantage of the carbon reduction benefits of E.V.s, decarbonising the electric grid and preparing for increased electricity demand are critical aspects that will need to be considered. The levels of greenhouse gases vary across the different states, which means that the impact of vehicle electrification is going to vary from state to state as well. 

Moreover, the effectiveness of EVs in reducing greenhouse gas emissions heavily depends on the carbon intensity of the electricity used to charge them. As such, the decarbonization of the electric grid becomes a pivotal factor in realising the full environmental benefits of vehicle electrification. This underscores the importance of integrating renewable energy sources into the grid and investing in smart grid technologies to manage the increased load from EV charging, ensuring that the transition to electric vehicles contributes positively to the nation's climate goals.

There have been various studies and models conducted into how greenhouse gas emission levels can be reduced in the transportation sector. Researchers have now developed a new model of the U.S. LDV fleet, which quantifies the impact of LDV electrification on greenhouse gas emissions and evaluates the emissions reduction with short-term Intergovernmental Panel on Climate Change (IPCC) carbon reduction targets and U.S. climate goals. 

What Previous Studies Have Looked at? 

Different models have been created that have looked at LDV fleet greenhouse gas emissions on a national level, but these have primarily focused on 2050 targets. It has been analysed by Alarfaj et al. [1] that 80-90% decarbonisation is possible by 2050, but attaining these targets is likely to rely on reducing the number of miles travelled by vehicles as well as electrification. 

Another study performed by Milovanoff et al. [2] found that around 90% of LDV fleets on the road would need to be electrified by 2050 to meet the 2°C climate targets, whereas Zhu et al. [3] found in another study that 100% of LDV sales would need to be E.V.s by 2040 to stay within the 2°C target. 

All these studies have used a bottom-up approach that considered the fleet emission under different scenarios to determine the electrification targets. However, all these studies noted that there are going to be challenges ahead brought about by long fleet turnover timelines and the technical need for widespread vehicle electrification and electric grid decarbonisation. 

New Study Taking a Different Approach 

Woody et al. [4] have now chosen to take a top-down approach and used the ideal goals and proposed regulations as the starting point―which is 50% electrification sales nationwide by 2030 and 67% by 2032―alongside current trends to see what the emissions would look like if these goals were met. The models used a base scenario for the model that is consistent with both goals. 

There are currently 15 states in the U.S. that have adopted more aggressive sales goals of 67% by 2030 rather than 50%, and some are aiming for 100% by 2035 based on the Clean Air Act. Due to the state-to-state variances, the researchers modelled each state individually instead of looking at the U.S. as a whole. The model used by the researchers uses weighted averages to accommodate the E.V. sales targets and includes more aggressive grid decarbonisation scenarios. This approach is new to these studies, and it was taken to show the impact that both E.V. adoption and grid emissions have on LDV emissions at the state level compared to nationally. 

The model in the latest study evaluated the vehicle electrification goal in relation to the economy-wide emissions goal, and it also considered the emissions from vehicle fuels, electricity production and vehicle production. Using a vehicle fleet model and life cycle emission model to predict sales, stock and emissions, the model was designed to account for state-level variability, and the model was subsequently applied to each individual state. From here, different grid development scenarios were explored to see what electrification and decarbonisation efforts―such as reducing vehicle size and mileage as well as accelerating the retirement of existing vehicles―could achieve if the current U.S. vehicle electrification goal meets the U.S. climate goals. 

Additionally, the adoption of electric vehicles alone will not suffice to meet the ambitious climate targets set for the transportation sector. Complementary strategies such as promoting public transportation, encouraging carpooling, and developing urban infrastructure that supports walking and cycling can significantly reduce vehicle miles travelled (VMT), further contributing to emission reductions. Implementing policies that incentivise these behaviours can help accelerate the shift towards a more sustainable and environmentally friendly transportation system.

What the Recent Study Has Added to the Debate 

The study showed that meeting the vehicle electrification sales goal and LDV fleet turnover should result in a reduction in emissions of around 25% by 2030. This is shorter than the 50% goals set out for the economy-wide emission reduction goal, but the emissions could drop by around 45% in 2035 if vehicle electrification is implemented alongside grid decarbonisation.  

The overarching results of the study show that to meet the goal demands, the transition to electric vehicles needs to be implemented alongside grid carbonisation, as well as other emission-reducing efforts such as decarbonising liquid fuels, reducing travel demand and using greener transport modes (i.e., mass transport modes) where possible, and retiring non-electric LDV fleet vehicles much quicker than originally planned. 

It is also critical to address the disparities in EV adoption across different states to ensure equitable access to the benefits of electrification. Financial incentives, expanding charging infrastructure, and targeted educational campaigns can play a significant role in overcoming barriers to EV adoption, particularly in underserved communities. By fostering an inclusive approach to vehicle electrification, policymakers can ensure that the transition to electric vehicles benefits all segments of the population, thereby enhancing the social acceptability and success of these initiatives.

Strategies for Equitable EV Adoption and Immediate Emission Reduction

While these are the long-term strategies that need to be met to achieve the emission targets, there are other short-term goals that could be implanted in the meantime (before this transition has been completed) that could help to reduce emissions and provide a start towards the goals. These short-term emission reduction strategies include reducing vehicle size vehicle production emissions, improving fuel economies, increasing the use of low-carbon fuels, and reducing the number of miles vehicles do. 

The difference between the state-level models and national fleet models shows that existing models that only focus on the national emission levels are underestimating the emission savings of electrification in the short term. However, both models converge more when grid decarbonisation is also factored in. 

The study has shown that considerations need to be made at the state level as well as the national level when it comes to calculating emission savings in the coming years. While electrification of vehicles will play a big part in reducing emissions, it is likely that real-world emission savings will fall short by 2030 and 2035 unless grid decarbonisation and fleet retirement are taken into account and widely implemented. Beyond 2035, it’s thought that if the predicted trajectories of vehicle electrification and grid decarbonisation continue the same path, there will be further accelerations towards LDV emission reduction that will help to contribute towards longer-term carbon neutrality goals. 

References: 

1. Alarfaj A. F. et al., Decarbonizing U.S. passenger vehicle transport under electrification and automation uncertainty has a travel budget. Environ. Res. Lett. 15, (2020), 0940c2. 
2. Milovanoff, A. et al., electrification of light-duty vehicle fleet alone will not meet mitigation targets. Nat. Clim. Chang. 10, (2020), 1102–1107. 
3. Zhu, Y. et al., Reducing Greenhouse Gas Emissions from U.S. Light-Duty Transport in Line with the 2 °C Target. Environ. Sci. Technol. 55, (2021), 9326–9338. 
4. Woody M. et al., Decarbonization potential of electrifying 50% of U.S. light-duty vehicle sales by 2030, Nature Communications, 14, (2023), 7077.