Kiera Jefferson
The transport sector is a significant contributor to air pollution and greenhouse gas emissions, with road vehicles being the primary source of transportation emissions. In the United States, the transportation sector is the largest contributor to greenhouse gas emissions, accounting for about 28% of total US greenhouse gas emissions. Cars, trucks, commercial aircraft, and railroads all contribute to transportation sector emissions. The US Environmental Protection Agency (EPA) and the Department of Transportation (DOT) have implemented regulations to reduce greenhouse gas emissions and improve fuel economy in the transportation sector, with a focus on cars, light trucks, and heavy-duty trucks. While there are efforts to reduce emissions, the demand for transportation is expected to grow worldwide, leading to a potential increase in transport emissions.
| Characteristics | Values |
|---|---|
| Greenhouse gas emissions from transportation as a percentage of total US emissions | 28% (largest contributor) |
| Increase in GHG emissions in the transportation sector between 1990 and 2022 compared to other sectors | Highest in absolute terms |
| Largest sources of transportation emissions | Cars, light trucks, heavy-duty trucks, commercial aircraft, railroads |
| Projected reduction in GHG emissions over the lifetime of light-duty vehicles sold between 2027 and 2032 | 7 billion metric tons |
| Projected reduction in GHG emissions over the lifetime of vehicles built under Phase 3 Heavy-duty GHG regulations | 1 billion metric tons |
| Average emissions of the most popular size car in 2020 per vehicle mile | 0.60 pounds of CO2 |
| Average emissions of a category of large pickup trucks built in 2020 per vehicle mile | 1.18 pounds of CO2 |
| Percentage of CO2 emissions from transportation in 2016 | 21% |
| Percentage of CO2 emissions from energy production in 2018 | 24% |
| Percentage of global energy-related CO2 emissions from transport in 2010 | 23% |
| Percentage of end-use energy emissions from transport in 2010 | 28% |
| Percentage of end-use energy consumption from urban transport in 2010 | 40% |
| Percentage of global CO2 emissions from transportation in 2023 | 16% (second-largest source) |
| Global transportation CO2 emissions in 2023 | 8.4 billion metric tons |
| US transportation CO2 emissions as a percentage of total global emissions in 2021 | 12% (second-largest contributor) |
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What You'll Learn
- Cars, trucks, aircraft, and railroads are the main sources of transport emissions
- Light-duty vehicles are the primary source of transport emissions
- Transport demand is expected to increase with global population growth
- Transport is a significant contributor to air pollution and health risks
- Strategies to reduce vehicle miles travelled can lower emissions
Cars, trucks, aircraft, and railroads are the main sources of transport emissions
Transportation is a major source of air pollution and emissions that contribute to climate change in the United States. Cars, trucks, aircraft, and railroads are the main sources of transport emissions.
Cars and trucks are a significant source of pollution in the US. The burning of fossil fuels by motor vehicles releases carbon dioxide, a greenhouse gas, into the atmosphere. In addition to carbon dioxide, cars and trucks emit toxic air pollutants such as benzene, acetaldehyde, and 1,3-butadiene, which are linked to different types of cancer. Cars and trucks also emit nitrogen oxides, which can cause lung irritation and weaken defences against respiratory infections. Furthermore, marginalized communities, particularly those of colour and low-income communities, are disproportionately exposed to higher levels of air pollution as they are often located near heavily travelled roadways.
Aircraft are also a major contributor to transport emissions. Airplanes emit gases such as carbon dioxide, water vapour, nitrogen oxides, and carbon monoxide, as well as atmospheric particulates such as incompletely burned hydrocarbons, sulfur oxides, and black carbon. The aviation industry's emissions are expected to grow, with estimates suggesting they could account for 3.5% of global CO2 emissions by 2030. Airports also generate significant water pollution due to their handling of jet fuel, lubricants, and other chemicals.
Railroads are another source of transport emissions, particularly in the US where the freight rail system emits more carbon pollution than many states. More than 13 million people in the US are directly impacted by locomotive pollution, with people of colour and lower-income individuals bearing the brunt of the pollution from trains and truck routes that run through or parallel to their communities. The rail industry has been resistant to decarbonization efforts, but there is hope that new regulations will help reduce their emissions and improve air quality for the communities affected.
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Light-duty vehicles are the primary source of transport emissions
The transportation sector is the largest contributor to US greenhouse gas (GHG) emissions, accounting for about 28% of the total. Within this sector, light-duty vehicles are the primary source of transport emissions. Cars, SUVs, and light-duty trucks fueled by gasoline, diesel, and E85 emit both GHGs and smog-forming pollutants from their tailpipes. These vehicles, which include sport utility vehicles, crossover utility vehicles, minivans, and pickup trucks, accounted for 58% of emissions in the transportation sector in 2019.
The average fuel economy of new light-duty vehicles has improved over time, rising from 20 miles per gallon in 2005 to 25 miles per gallon in 2021. This has helped to reduce emissions, even as travel by car and truck has increased. The EPA has also played a role in reducing emissions by lowering the amount of pollution that light-duty vehicles are permitted to emit since the first standards were set in 1970. These standards have been strengthened over time, with the current Tier 3 standards being gradually phased in starting in the 2017 model year.
Despite these improvements, light-duty vehicles still contribute significantly to transport emissions. The type of fuel used and the fuel efficiency of the vehicle are important factors in determining emissions per passenger-mile. For example, the most popular size car in 2020 emitted 0.60 pounds of CO2 per vehicle mile, while a category of large pickup trucks emitted nearly twice that amount (1.18 pounds of CO2 per vehicle mile). Additionally, economic growth and the price of motor vehicle fuels can affect total vehicle miles traveled and, consequently, total CO2 emissions in the transportation sector.
To further reduce emissions from light-duty vehicles, the EPA has set GHG emissions and fuel economy standards for model years 2027-2032. These standards are projected to cut 7 billion metric tons of GHG emissions over the lifetimes of the vehicles sold during this period. Electrification of light-duty vehicles can also help to reduce emissions, as electric vehicles are more efficient than those powered by fossil fuels.
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Transport demand is expected to increase with global population growth
The transportation sector is a major contributor to pollution in the United States. Greenhouse gas (GHG) emissions from transportation account for about 28% of total US greenhouse gas emissions, making it the largest contributor to US GHG emissions. Cars, trucks, commercial aircraft, and railroads are among the sources of these emissions.
The growth in transport demand has already been observed in various modes of transportation. For example, global demand for public transport grew by 4% per year between 2012 and 2017, with bus rapid transit, metro rail, and light rail transit expanding in different regions. Motorised two-wheelers, such as mopeds and motorcycles, also experienced significant growth in India and Vietnam during this period.
The increase in transport demand can have a significant impact on pollution levels. As more people rely on transportation, the energy consumption and fuel usage associated with this sector will rise. This can lead to a surge in coal usage and an increase in the consumption of oil, electricity, natural gas, and crude oil, all of which contribute to adverse climate effects.
However, it is important to note that there are opportunities to mitigate the environmental impact of increasing transport demand. The development and adoption of low-carbon fuels, improved vehicle technologies, strategies to reduce vehicle miles traveled, and more efficient operation of vehicles can all contribute to reducing greenhouse gas emissions from transportation. Additionally, initiatives like SmartWay by the EPA aim to improve supply chain efficiency, reduce greenhouse gases, and address air quality challenges in the freight transportation sector.
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Transport is a significant contributor to air pollution and health risks
The transport sector is a significant and growing contributor to particulate air pollution, which is most closely linked to air-pollution-related deaths and illnesses. An estimated 4.2 million premature deaths are attributed to ambient (outdoor) air pollution. Higher air pollution concentrations increase the risk for cardiovascular and respiratory diseases, cancer, adverse birth outcomes, and are associated with higher death rates. Environmental noise exposure is another health risk, increasing the risk of ischaemic heart disease, sleep disturbance, cognitive impairment among children, annoyance, stress-related mental health risks, and tinnitus. These risks account for at least one million healthy life-years lost every year from traffic-related noise in high-income European countries.
While transportation continues to contribute a large percentage of US emissions, there are opportunities for the sector to reduce greenhouse gas emissions. Low-carbon fuels, new and improved vehicle technologies, strategies to reduce vehicle-miles travelled, and operating vehicles more efficiently are all approaches to reducing greenhouse gases from transportation. For example, the average fuel economy of new light-duty vehicles (cars and light-duty trucks) rose from 20 miles per gallon in 2005 to 25 miles per gallon in 2021. The EPA and DOT have also issued joint rule-making that set GHG emissions and fuel economy standards for cars, light trucks, and heavy-duty trucks, which are projected to cut 7 billion metric tons of GHG emissions over the lifetimes of the vehicles sold in model years 2027-2032.
Major technological innovations can also help to offset the rise in transport demand. The rise of electric vehicles offers a viable option to reduce emissions from passenger vehicles, although emissions attributable to electric vehicle use depend on the emissions from generating the electricity used to power them. In some parts of the country, electricity can be generated with much lower CO2 emission rates than others, due to the use of more renewables and natural gas than coal.
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Strategies to reduce vehicle miles travelled can lower emissions
The transportation sector is the largest contributor to US greenhouse gas (GHG) emissions, accounting for about 28% of total US GHG emissions. Cars, trucks, commercial aircraft, and railroads are among the sources of these emissions. Most emissions in this sector come from cars and trucks, with motor vehicles accounting for 83% of CO2 emissions from transportation in 2019.
The US government has set targets to reduce vehicle miles traveled (VMT) and, in turn, emissions. Strategies to reduce VMT can be implemented at the state level, with some states already experimenting with innovative programs. For example, Seattle has incentivized remote working and carpooling, helping to lower per-capita VMT by about 17% from 2005-2018. Similarly, Paris has implemented a range of policies, resulting in Parisians driving 45% less than they did in 1990.
The Coalition for Clean Air is an organization working to reduce VMT in California. They support the construction of projects that reduce reliance on single-occupancy vehicles, such as protected bike lanes, sidewalks, and bus shelters. They also advocate for better land use and transportation practices, such as the creation of 15-minute cities where all basic needs are located within a 15-minute reach, reducing the need to travel long distances.
Other strategies to reduce VMT include:
- Congestion pricing tolls: Implementing congestion pricing can reduce congestion and encourage the use of alternative modes of transportation.
- Mass transit finance: Investing in public transportation can make it more accessible and affordable, encouraging people to use it instead of driving.
- Remote work incentives: Encouraging remote work can reduce the number of commuters on the road.
- Carpooling: Promoting carpooling can reduce the number of vehicles on the road and is especially effective when coupled with incentives for using low-emission or zero-emission vehicles.
- Improving fuel efficiency: Increasing the fuel efficiency of vehicles can help reduce emissions, even as vehicle miles traveled increase.
- Zero-emission vehicles (ZEVs): While ZEVs do not solve all air quality issues, they are critical to reducing greenhouse gas emissions and combustion-related pollutants.
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Frequently asked questions
Greenhouse gas emissions from transportation account for about 28% of total US greenhouse gas emissions, making it the largest contributor to US GHG emissions.
Cars, trucks, commercial aircraft, and railroads are all significant sources of transportation sector emissions. Cars and trucks are the primary sources, with passenger cars being the largest contributor.
The EPA has introduced regulations to improve fuel efficiency and reduce emissions. Low-carbon fuels, new vehicle technologies, and strategies to reduce vehicle miles travelled can all help. Electric vehicles are also a viable option.
Transport-related air pollution is linked to 4.2 million premature deaths worldwide. Higher air pollution concentrations increase the risk of cardiovascular and respiratory diseases, cancer, and adverse birth outcomes.
