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Transportation: A blindspot in US climate policy

by Kira McDonald

November 2, 2023

Key Takeaways

  • Emissions from electricity generation are beginning to decline, but transportation emissions continue to rise. Transportation is now the leading source of emissions in the United States, comprising 29% of the US total.

  • Relying on a personal electric vehicles-first strategy to decarbonize the sector will be slow and inadequate. Households keep cars for close to 10 years, meaning slow turnover rates. A transition solely focused on EVs would also dramatically increase the need for electricity production and reinforce highway and road building, which themselves are carbon intensive processes, in comparison to a more blended strategy that prioritizes mass and active transit strategy. 

  • The Bipartisan Infrastructure Law (BIL) included significant funding for state Departments of Transportation, but with few guardrails on how to spend the money. States serious about climate should spend the maximum allowable amounts of BIL funding on public/active transit and refrain from highway expansions. This can make decarbonization more achievable, as well as provide additional benefits in terms of health, public safety, and accessibility.

Major climate policies are finally being passed in the United States, and emissions are beginning to decline in some economic sectors. But progress in some areas is still paired with backsliding in others: as emissions from electricity generation have declined, those from transportation have mostly continued to rise. Transportation is now the leading source of emissions in the United States, comprising 29% of the US total. Within this sector, light-duty vehicles (LDVs) – cars, SUVs, and pickup trucks – comprise the majority (58%) of emissions, followed by heavier trucks (23%) and aircraft (8%). 

Policy approaches to decarbonizing transportation in the US have focused overwhelmingly on EVs – but this strategy is not likely to work. Climate scientists have consistently stressed that decarbonization strategies that start and end with electric vehicles will not succeed in keeping climate change within 2 degrees of warming – let alone 1.5. This finding has repeatedly been documented:  EVs alone are inadequate to decarbonize transportation on the necessary timeline.

This post summarizes research and data on the problems with a narrow focus on fuel switching to drive down emissions from transportation, and then provides an overview of some essential policies to help advance decarbonization swiftly and equitably.


EVs are inadequate for decarbonization

The speed of eliminating emissions by electrifying light duty vehicles (LDVs) is limited by the turnover of the existing vehicle fleet and the emissions intensity of the electricity grid. EVs accounted for only 5.6% of new car sales in the US in 2022. Households in the US keep vehicles for a decade on average, and, meaning EVs will only gradually comprise larger shares of vehicles in the United States, even as their share of sales finally begins to increase further. Meanwhile, as EVs sales rise, supply chain bottlenecks, particularly of “critical minerals” are likely, especially if subsidies for personal EVs are not paired with policies to reduce reliance on cars, limit new EV battery sizes, and support recycling. Such bottlenecks would further slow the rate of EV adoption. Widespread adoption of EVs will also massively increase the demand for electricity while the transition to a decarbonized electricity grid is still underway, massively increasing the magnitude of that challenge. According to recent research, “closing the mitigation gap solely with EVs would require…half of national electricity demand.” Meanwhile, producing EVs and building and maintaining roads, highways, and parking lots are all emissions intensive processes, and shifts in land use from natural landscapes to car infrastructure, including lithium mines, are set to further increase emissions by destroying important carbon sinks.

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The inadequacy of our EVs-first strategy is becoming increasingly visible not only in the work of climate modelers, but in sectoral emissions data: as emissions from the electric power generation – the other highest-emitting sector – have declined, transportation emissions have, apart from a dip from Covid-19, continued to rise (figures above).

Policymakers serious about climate change must reckon with the reality that effective decarbonization of this sector will require a more robust set of policies than the current near-singular focus on EVs. More robust strategies for transportation decarbonization would also yield a host of co-benefits—in terms of ecosystem preservation and global justice; public health and life expectancy; economic equality; financial and time savings; better mental health and overall happiness; and more.


Bending down the curve

Researchers repeatedly stress that effective decarbonization policy requires a range of complementary policies to meet emissions goals. In particular, transportation decarbonization strategies must emphasize mode shift to more efficient modes of transportation (such as public and active transit) and increased fuel efficiency standards – in addition to electrification of the LDV fleet. While the range of policies and implementation strategies that could help realize these goals is vast, some essential policies are outlined below:


Implement fuel efficiency and size regulations.

While emissions from electricity generation fell substantially during the 2010s, transportation emissions increased. This increase followed a widening of the “SUV loophole” that allowed larger vehicles to meet more relaxed fuel efficiency standards relative to smaller cars. Models of decarbonization pathways for transportation have repeatedly stressed that closing this loophole and introducing more stringent fuel efficiency standards for internal congestion engine (ICE) cars are necessary for the US transportation sector to stay within an emissions budget consistent with even 2 °C of warming. 

Efficiency is also important for EVs, not only to save electricity, but also because more efficient EVs will require smaller batteries for the same range. Larger batteries require more “critical minerals,” and increasing the volume of minerals required for an EV transition is set to worsen supply chain bottlenecks and negative social and environmental impacts from mineral mining. 

US safety standards also contribute to the perverse regulatory incentives for larger cars. US safety ratings are based only on the safety of vehicle occupants, and not those outside the vehicle, for whom larger vehicles are more deadly. Now new LDVs in the US are larger than ever, and their size – “the car safety feature that kills the other guy” – is a major factor in the exceptionally high rate of traffic deaths in the United States compared to other countries.

Larger vehicles cause not only increased traffic fatalities, higher emissions, and greater “critical mineral” requirements, but also faster wear and tear on road infrastructure and produce more pollution, particularly from tire and brake wear. Car tires are a particularly massive source of air and water pollution, with microplastics from tires comprising up to seventy-eight percent of microplastics in the ocean, and air pollution from tire and brake wear are a growing public health concern. Pollution from car brakes and tires already exceeds tailpipe pollution, and it is set to worsen with EVs. 

Finally, Because used US vehicles tend to be resold later in other, frequently poorer countries, trucks and SUVs sold in the US will also continue to contribute to global emissions, particulate and microplastic pollution, and unnecessary traffic deaths even after they are off US roads.

At the federal level, the “SUV loophole” should be closed: fuel efficiency standards should not vary by vehicle size. Safety ratings should be revised to reflect danger posed to those outside the vehicle. Registration, parking, or other fees that scale with vehicle size can help discourage larger vehicles (such policies are being considered in Colorado and Washington DC). Warnings of the danger larger vehicles can pose to pedestrians or others outside the vehicle could also be required in car advertisements or at points of sale.


Shift investment from car infrastructure to public and active transit.

Many cities and states are still pursuing transportation priorities—particularly widened highways—that will increase emissions, even where their mayors or governors have pledged to work to protect the climate. At the federal level, the Biden Administration has realized a significant climate win with the Inflation Reduction Act, but their other landmark policy, the Bipartisan Infrastructure Law (BIL) will either increase or decrease emissions, depending on how the infrastructure money is spent. Specifically, analysis finds that if states use more is used on highway expansions, the BIL will increase GHG emissions; if states transfer funds to transit projects and other climate-friendly investments when possible, it will decrease emissions.

Both BIL spending and other investments should prioritize active and transit infrastructure over car-exclusive infrastructure that will lock in higher emissions. States serious about climate should spend the maximum allowable amounts of BIL funding on public/active transit and refrain from highway expansions. Investments in inter-city rail would also allow headway on the decarbonization of on-road freight and air travel, the two leading sources of transportation emissions after LDVs.

Research has shown that public transit can be efficient and convenient even in lower density metropolitan areas, as long as key qualities are achieved, including high frequency service and/or timed transfers, integrated fares and ticketing, and the coordination of different modes within a unified network. Notably, these qualities all depend on a strong public body capable of oversight and integrated planning of the transit network. Finally, to balance decades of massive subsidies for auto infrastructure, the federal government should also provide operating funding for local transit to plan and manage regional networks and increase frequency and regularity. 


Impose congestion charges and create low-traffic areas.

A meta-analysis of policies to reduce driving found that congestion charges, or tolls for personal cars entering a city center, were highly effective for reducing car use. Low-traffic areas, created through car-free streets, car-free zones in city centers, reductions in parking spaces, and expanded pedestrian and bike networks, were also effective.

Reducing the volume of cars removes congestion, pollution, and danger so that options such as walking, biking, and buses are safer, faster, and more pleasant. In Brussels, car traffic was reduced by 25% in the span of only a year, with a concurrent 36% increase in bicycling with the implementation of these and other measures. Similar policies have also been successful reducing car traffic and increasing active transportation on a very short timeline in many other cities, including Vienna, London, and Paris.

These might be thought of as the “stick” policies to encourage modeshift, compared to the “carrot” policies of improved public and active transit. Research shows that both sets of policies are necessary to achieve modeshift. These “stick” policies can be initially met with hesitance or resistance, but they consistently prove extremely popular once implemented, due to massive benefits in terms of greater quality of life and decreased traffic congestion.


Incentivize density and diversity of land use and other urban design policies.

Certain features of a built environment can shift a meaningful share of trips to sustainable travel options and reduce car dependence, even in the absence of major public transit infrastructure. Features such as connected street grids with shorter blocks, larger sidewalks, more tree coverage, less on- and off-street parking, and slower speed limits facilitate walking as a form of transportation by making trips more convenient and pleasant. Policymakers can also increase the attractiveness of active and public transportation through land use policy that permits higher density and more mixed use uses, and the elimination of minimum parking requirements.


Develop supportive policies for bikes, E-bikes, and other micromobility. Bikes, e-bikes, and other forms of micromobility are a tremendous opportunity to quickly reduce transportation emissions while realizing a multitude of co-benefits. Even with massive subsidies for electric LDVs and a superabundance of dedicated car infrastructure relative to dedicated bike infrastructure, e-bikes are still outselling EVs in the US. Bikes and E-bikes have enormous potential to quickly cut transportation emissions and realize the reductions in car travel required to stay within sectoral emissions targets. 


But bikes and e-bikes require supportive policies and infrastructure to realize this potential. While some media have portrayed e-bikes as dangerous or risky, this risk stems from their interactions with cars, rather than the bikes themselves. Meanwhile surveys have found that safety concerns around car traffic are an enormous barrier to biking or even walking for transportation. 

Many of the above policies would also support bike and e-bike adoption. Revising car safety standards to consider those outside the vehicle, implementing low-traffic corridors, lowering speed limits, and building low-stress bike networks would decrease the danger and stress of biking and increase uptake. In addition to these policies, subsidies for bikes and e-bikes should be comparable to those for EVs; successful e-bike incentives should be expanded and replicated. Bike lanes should be designed to allow a range of users by speed and ability, with good visibility and room for passing or riding side-by-side. Finally, at the federal or local levels, e-bike batteries should be regulated to meet safety standards.


Create car share programs. Reducing car use is necessary to meet sectoral climate goals and realize major co-benefits, but eliminating car use is not. Car sharing programs can be extremely useful to provide flexibility and car access for trips for which they are the necessary or most convenient option. Car sharing can have mixed effects on ownership and use, but are more likely to be effective in the presence of other complementary policies. When deployed effectively, car share systems are a promising path to reduce embodied emissions and mining impacts from new vehicle and battery manufacturing. 


Final Thoughts

Reducing car use is essential to meeting sectoral emissions targets for transportation. Transportation is the largest source of emissions in the US and LDVs comprise the majority of emissions within the sector. Supportive policies to reduce LDV emissions will often have complementary effects on other sources of emissions. Greater investment in a national rail network that could accommodate both more passenger and freight movement, and help reduce emissions from both those sources. Denser built environments, which tend to be more supportive of public and active transit, will also mean more land can be retained for natural ecosystems that function as carbon sinks, and are also often associated with lower life-cycle emissions from housing (depending also on other factors of the housing types).

For social and institutional factors, rather than technological reasons, transportation likely faces the greatest barriers towards decarbonization. But the stakes are high, and if the US stays on its current trajectory, transportation emissions are bound not only to surpass our country’s sectoral carbon budget, but also to increase catastrophically and avoidably in other countries as well, as higher-emitting used LDVs are re-sold abroad, economic pressures on the car industry spur global LDV growth, and other forms of globalized carbon lock-in proceed.

Beyond climate change and the other issues mentioned, our transportation system is also intimately connected to a host of other social and economic issues. The construction of car dependency in the United States was inextricable from the creation of highly racialized urban geographies—with highway construction, urban renewal programs, and massive, racially-exclusive subsidies for car-oriented suburban developments underpinning continuing segregation by race and class. Subtle aspects of the built environment, such as cul-de-sacs or street discontinuities function as “exclusionary urban design tactics” that can still help uphold segregation in US cities. These same features of the built environment also help construct car dependence by reducing the convenience and usefulness of alternatives. Particularly in the context of the suburbanization of lower-income Americans, thoughtful implementation and policy design would be necessary to help realize the opportunity, but reversing the course on car dependency would pose a major opportunity to partially redress major historical harms. 

The US transportation sector is currently far from a plausible decarbonization pathway. Decarbonization strategies must immediately expand from a near-singular focus on EVs in order to move towards less catastrophic emission pathways. Although the task of reducing emissions in this essential sector is massive, this post aims to provide an overview of promising approaches for policymakers and advocates serious about addressing the climate crisis while realizing the multitude of co-benefits possible from decarbonizing the sector.

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