Bronte Wells
The transport sector is a leading source of air pollution and a significant contributor to climate change. Transportation is responsible for a large percentage of primary pollutants, including greenhouse gas emissions (GHG), particulate matter (PM), nitrogen oxides (NOx), and carbon monoxide (CO). In the United States, transportation is the largest contributor to GHG emissions, accounting for about 28% of the total. Heavy-duty vehicles, such as trucks and buses, make up only 10% of all vehicles on the road but produce a disproportionate amount of global warming emissions, NOx emissions, and PM2.5 emissions. Traffic congestion further exacerbates vehicle emissions and degrades air quality, posing health risks to drivers, commuters, and individuals living near major roadways. The transition to electric vehicles and the development of infrastructure for safer walking and cycling are important steps towards reducing transportation's impact on the environment and human health.
| Characteristics | Values |
|---|---|
| Percentage of total US greenhouse gas emissions attributable to transportation | 28% |
| Percentage of global warming emissions attributable to heavy-duty vehicles | 25% |
| Percentage of NOx emissions attributable to heavy-duty vehicles | 45% |
| Percentage of direct PM2.5 emissions from on-road vehicles attributable to heavy-duty vehicles | 60% |
| Percentage of all passenger-miles travelled in personal vehicles in 2019 | 81% |
| Percentage of global energy-related CO2 emissions attributable to the transport sector in 2010 | 23% |
| Percentage of end-use energy emissions attributable to the transport sector in 2010 | 28% |
| Percentage of end-use energy consumption attributable to urban transport in 2010 | 40% |
| Percentage of domestic emissions from burning fossil fuels attributable to transportation | two-fifths |
| Percentage of electric vehicle emissions attributable to generating electricity | Variable |
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What You'll Learn
Transportation is the largest contributor to US GHG emissions
Greenhouse gas (GHG) emissions from transportation account for about 28% of total US greenhouse gas emissions, making transportation the largest contributor to US GHG emissions. The transportation sector includes cars, trucks, commercial aircraft, and railroads, among other sources. Over 94% of the fuel used for transportation is petroleum-based, which includes primarily gasoline and diesel, and results in direct emissions.
While transportation is the largest contributor to US GHG emissions, it is important to note that not all emissions from transportation are included in this figure. The US GHG Inventory, for example, does not include emissions from non-transportation mobile sources such as agriculture and construction equipment. Additionally, the Inventory's section on Fossil Fuel Combustion considers indirect emissions from distributed electricity, which can impact the ranking of emission sources. When considering indirect emissions, transportation is the third-largest contributor to US GHG emissions, after electricity production and industry.
Transportation emissions have been increasing over time. Between 1990 and 2022, GHG emissions in the transportation sector increased more in absolute terms than in any other sector. This increase is attributed to a variety of factors, including increased demand for travel, population growth, economic growth, urban sprawl, and periods of low fuel prices. The number of vehicle miles traveled (VMT) by light-duty motor vehicles (passenger cars and light-duty trucks) increased by 47% during this period.
The good news is that there are opportunities to reduce greenhouse gas emissions from transportation. For example, the EPA has implemented programs to reduce GHG emissions from the transportation sector, such as setting GHG emissions and fuel economy standards for cars, light trucks, and heavy-duty trucks. Consumers can also play a role by choosing environmentally friendly vehicles that have better fuel economy and lower emissions. Electric trucks and buses, for example, have significantly lower global warming emissions than vehicles powered by fossil fuels. Policies and investments from federal, state, and municipal governments can further accelerate the transition to a zero-emissions transportation system.
In addition to GHG emissions, transportation also contributes to other types of air pollution, such as particulate matter (PM), nitrogen oxides (NOx), and sulfur dioxides. These pollutants have significant impacts on human health and the environment. Traffic congestion, for example, increases vehicle emissions and degrades ambient air quality, leading to excess morbidity and mortality for drivers, commuters, and individuals living near major roadways.
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Health risks of congestion and traffic pollution
Transportation is a major contributor to air pollution, which carries significant risks for human health and the environment. Greenhouse gas (GHG) emissions from transportation account for about 28% of total US greenhouse gas emissions, making it the largest contributor of US GHG emissions. Heavy-duty vehicles make up only about 10% of all vehicles on the road, yet they generate over 25% of global warming emissions, almost 60% of direct PM2.5 emissions from on-road vehicles, and significant amounts of air pollution.
Traffic congestion increases vehicle emissions and degrades ambient air quality, with studies showing excess morbidity and mortality for drivers, commuters, and individuals living near major roadways. The increasing severity and duration of traffic congestion have the potential to greatly increase pollutant emissions and degrade air quality, particularly near large roadways. These emissions contribute to increased health risks, including respiratory and cardiovascular issues, for those living or working nearby.
The health risks from congestion can be estimated using epidemiological studies that include indicators such as time spent in congestion. These studies can provide tailored dose-response relationships that can be used in risk assessments. For example, a 30-minute daily travel delay can account for 21% of the exposure to benzene and 14% of PM2.5 exposure for a typical working adult on weekdays. The health impacts of congestion can also be monetized, with one study estimating the public health cost of mortality attributable to congestion in 83 US cities in 2000 to be $31 billion.
To reduce emissions and health risks, clean vehicle and fuel technologies, as well as policies and investments to promote zero-emission transportation, are essential. Electric trucks and buses, for instance, have significantly lower global warming emissions than vehicles powered by fossil fuels.
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Electric vehicles reduce emissions
Transportation is a major contributor to air pollution, with greenhouse gas (GHG) emissions from this sector accounting for about 28% of total US greenhouse gas emissions. This includes emissions from cars, trucks, and buses, as well as airplanes, trains, and ships. Heavy-duty vehicles, for instance, make up only about 10% of all vehicles on the road, yet they generate over 25% of global warming emissions. Traffic congestion also increases vehicle emissions and degrades ambient air quality, with studies showing excess morbidity and mortality for those living near major roadways.
Electric vehicles (EVs) are an effective way to reduce emissions from the transportation sector. They produce zero tailpipe emissions, which is a significant source of pollution from conventional vehicles. This means that even when accounting for electricity emissions from power plants, EVs are typically responsible for lower levels of GHGs than gasoline cars. In countries like France and Norway, where electricity comes from near-zero carbon sources such as hydroelectric or nuclear power, lifecycle emissions for EVs are much smaller.
EVs also have the advantage of being more energy-efficient than gasoline vehicles. They use approximately 87-91% of the energy from the battery for propulsion, compared to gasoline vehicles, which only convert about 16-25% of energy from gasoline. This higher efficiency results in lower fuel consumption, reducing dependence on foreign oil and saving consumers money.
While some argue that the manufacturing of EV batteries creates more carbon pollution than that of gasoline cars, this impact can be mitigated by using renewable energy sources for battery production. Studies have shown that producing batteries in plants powered by renewable energy can substantially reduce lifetime emissions. Additionally, as the Paris Agreement pushes for a less carbon-intensive electricity generation, the advantage of EVs over conventional vehicles will further increase.
Overall, electric vehicles play a crucial role in reducing emissions from the transportation sector, improving air quality, and mitigating the impacts of climate change. With the right policies and investments, a transition to a zero-emissions transportation system is achievable.
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Transport sector is the fastest-growing contributor to climate emissions
Greenhouse gas (GHG) emissions from transportation account for about 28% of total US greenhouse gas emissions, making transportation the largest contributor to US GHG emissions. Between 1990 and 2022, GHG emissions in the transportation sector increased more than in any other sector. Transport emissions, which primarily involve road, rail, air, and marine transportation, accounted for over 24% of global carbon dioxide (CO2) emissions in 2016. They are also expected to grow at a faster rate than any other sector, making the transport sector the fastest-growing contributor to climate emissions.
The main drivers of global transport energy growth are land transport, mostly light-duty vehicles such as cars, and freight transport. Heavy-duty vehicles make up only about 10% of all vehicles on the road, yet they generate more than 25% of global warming emissions, 45% of nitrogen oxide (NOx) emissions, and nearly 60% of direct PM2.5 emissions from on-road vehicles. Communities adjacent to ports and interstates bear the brunt of exposure to this dangerous air pollution.
Traffic congestion increases vehicle emissions and degrades ambient air quality, and studies have shown excess morbidity and mortality for drivers, commuters, and individuals living near major roadways. Higher air pollution concentrations increase the risk of cardiovascular and respiratory diseases, cancer, and adverse birth outcomes, and are associated with higher death rates.
To reduce transport emissions, cities should embrace automation, electrification, and ride-sharing. Research shows that these measures could cut transport emissions by 80%. Electric trucks and buses have significantly lower global warming emissions than vehicles powered by fossil fuels, and a growing number of cities are committed to 100% zero-emission transit buses in their fleets.
To limit global temperature increases, transport's reliance on fossil fuels needs to shift dramatically. Transitioning to zero-emission transport is crucial for a livable future, and improvements are needed in clean fuels, vehicle efficiency, urban planning, and how we move people and goods.
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Transport emissions and health risks
The transport sector is a leading source of greenhouse gas emissions, contributing about 28% of total US greenhouse gas emissions. It is the largest contributor to US GHG emissions, with emissions in the sector increasing more between 1990 and 2022 than in any other sector. Transport 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 outdoor air pollution, with higher concentrations increasing the risk of cardiovascular and respiratory diseases, cancer, adverse birth outcomes, and higher death rates.
Road transport is the largest contributor to climate change within the transport sector, with diesel traffic responsible for a substantial share of particulate matter emissions. Heavy-duty vehicles make up only 10% of all vehicles on the road, yet they generate over 25% of global warming emissions, almost 60% of direct PM2.5 emissions from on-road vehicles, and significant amounts of air pollution. Communities near ports and interstates bear the brunt of this dangerous air pollution.
Traffic congestion increases vehicle emissions and degrades air quality, with recent studies showing excess morbidity and mortality for drivers, commuters, and those living near major roadways. A 30-minute daily travel delay can account for a significant percentage of exposure to benzene and PM2.5 for a typical working adult. The health effects of traffic congestion are not yet well understood, but key factors affecting risks include traffic volume, speed, road type, emission factor, and meteorology.
Transport emissions include precursors of ground-level ozone, such as nitrogen oxides and carbon monoxide, which are particularly dangerous for vehicle operators and passengers in closed spaces. Carbon monoxide blocks oxygen from the brain, heart, and other vital organs when inhaled. Sulfur dioxide, formed by burning sulfur-containing fuels like diesel and coal, poses the largest health risk to children and asthmatics.
To reduce transport emissions and improve health, many cities are prioritizing public transport, bicycles, and pedestrian movement. Electric vehicles and buses are also being introduced, with cities like New York and Los Angeles committing to 100% zero-emission transit buses. These initiatives aim to reduce emissions and promote physical activity, which has been proven to help prevent and manage non-communicable diseases and improve mental health.
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Frequently asked questions
Transportation is responsible for about 28% of total US greenhouse gas emissions, making it the largest contributor of US GHG emissions.
Cars, trucks, commercial aircraft, and railroads are some of the sources that contribute to transportation end-use sector emissions.
Heavy-duty vehicles comprise only about 10% of all vehicles on the road, yet they generate more than 25% of global warming emissions, 45% of NOx emissions, and nearly 60% of direct PM2.5 emissions from on-road vehicles.
Higher air pollution concentrations increase the risk of cardiovascular and respiratory diseases, cancer, and adverse birth outcomes, and are associated with higher death rates.
