Katerina Swanson
Transport is a significant contributor to carbon emissions, with the transport sector accounting for around one-fifth of global carbon dioxide (CO2) emissions. In the US, the transport sector is the largest contributor to greenhouse gas emissions, making up about 28% of total US greenhouse gas emissions. This is largely due to the continued dependence of the transport sector on fossil fuels, with transport relying on oil products for nearly 91% of its energy. However, there are efforts to reduce emissions from transport, such as the use of electric vehicles, improved vehicle technologies, and strategies to reduce the number of vehicle miles travelled.
| Characteristics | Values |
|---|---|
| Percentage of global carbon dioxide emissions from transport | 24% of energy-related emissions, 28% of US emissions |
| Carbon dioxide emissions from transport in the US | Constitutes two-fifths of domestic emissions from burning fossil fuels |
| Carbon dioxide emissions from transport in the US in 2021 | 6% less than in 2005 |
| Carbon dioxide emissions from transport in the US between 1990 and 2022 | Increased more in absolute terms than any other sector |
| Carbon dioxide emissions from transport in the US in 2022 | Largest portion (28%) of total US GHG emissions |
| Carbon dioxide emissions from transport in the US in 2032 | Could be 6% higher than projected if real GDP is 8% higher than the Energy Information Agency's baseline scenario |
| Carbon dioxide emissions from transport in the US by 2030 | Projected to be half of 2021 levels |
| Carbon dioxide emissions from transport in the IEA's Net Zero Scenario by 2030 | Need to fall by around a quarter |
| Carbon intensity standards | Need to be tightened immediately for shipping |
| Carbon dioxide emissions from transport by road | Accounts for three-quarters of transport emissions |
| Carbon dioxide emissions from transport by road (breakdown) | 45.1% from passenger vehicles, 29.4% from trucks carrying freight |
| Carbon dioxide emissions from transport by aviation | Accounts for 11.6% of transport emissions |
| Carbon dioxide emissions from transport by rail | Lower than emissions from aviation |
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What You'll Learn
The transportation sector is the largest contributor to US emissions
Various strategies can be employed to reduce greenhouse gas emissions from the transportation sector. These include the use of low-carbon fuels, improved vehicle technologies, and strategies to reduce vehicle miles traveled, such as encouraging the use of public transport, walking, and cycling for shorter distances. Operating vehicles more efficiently is also crucial, and the EPA's SmartWay program helps freight companies improve supply chain efficiency and reduce emissions.
The electrification of vehicles is another important strategy. Electric vehicles emit less carbon dioxide than petrol or diesel cars, even when powered by a high-carbon electricity grid. However, the potential for hydrogen fuel or batteries to power long-distance road freight, aviation, and shipping is limited by the range and power requirements. Major technological innovations, such as electric vehicles, can help offset the rising demand for transport as the global population increases and more people can afford cars and flights.
To achieve significant emission reductions, a broad set of policies must be implemented to encourage shifts to less carbon-intensive travel options and improve energy efficiency across all transport modes. This includes tightening carbon intensity standards for shipping and encouraging the use of low-carbon fuels. The Congressional Budget Office projects that by 2030, CO2 emissions in the electric power sector will be halved compared to 2021 levels, which will further reduce emissions from electric vehicles.
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Passenger vehicles and freight trucks are the largest emitters
Road travel accounts for three-quarters of transport emissions, with most of this coming from passenger vehicles such as cars and buses (45.1%). The remaining 29.4% comes from freight trucks. Passenger vehicles emit about 400 grams of CO2 per mile, or about 4.6 metric tons of CO2 per year. The average freight truck in the US emits 161.8 grams of CO2 per ton-mile.
Freight transportation moves billions of tons of cargo around the world each year, and nearly all of it runs on oil and gas. Road vehicles like trucks and vans make up the majority (65%) of freight emissions. Strategies to reduce freight emissions include modern engines, low-carbon fuels, and more efficient practices such as using vehicle space more efficiently or reducing freight demand.
To reduce emissions from passenger vehicles, the world is shifting towards lower-carbon electricity sources and electric vehicles. The EPA's SmartWay light-duty program identifies the top-performing vehicles in terms of fuel economy and emissions to assist consumers in making environmentally friendly purchases.
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Traffic congestion increases emissions
Transportation is one of the largest contributors 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 transportation sector emissions. The burning of fossil fuels like gasoline and diesel releases carbon dioxide, a greenhouse gas, into the atmosphere.
The relationship between traffic congestion and emissions is complex. When congestion reduces the average vehicle speed below 45 mph, CO2 emissions tend to increase. This is because vehicles spend more time on the road, leading to higher emissions. However, moderate congestion that slows down traffic from speeds over 70 mph to a range of 45 to 55 mph can actually reduce CO2 emissions.
The impact of congestion on emissions is influenced by various factors, including individual driving behavior, vehicle and roadway types, and traffic conditions. For example, congestion can lead to more frequent speedups, slowdowns, stops, and starts, which increase emissions compared to "cruise" conditions, especially with high-power acceleration. Additionally, congestion diminishes the dispersion of vehicle-related pollutants as vehicle-induced turbulence depends on vehicle speed.
Overall, addressing traffic congestion through effective management strategies is essential to reducing emissions and improving air quality, particularly in areas with heavy traffic. By implementing congestion mitigation programs and considering the various factors that influence emissions, we can work towards lowering the environmental and health impacts associated with traffic congestion.
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Electric vehicles are a viable option to reduce emissions
Electric vehicles (EVs) are a viable option to reduce emissions. The transportation sector is the largest contributor to carbon emissions in the US, accounting for about 28% of total US greenhouse gas emissions. Cars, trucks, airplanes, and railroads are among the sources of transportation sector emissions.
EVs, including all-electric, plug-in hybrid (PHEV), and hybrid electric vehicles (HEVs), produce lower tailpipe emissions than conventional vehicles and zero tailpipe emissions when running on electricity. While electricity generation for EVs may create carbon emissions, this varies based on the energy source, with renewable sources like wind and solar producing no carbon pollution. In areas with relatively low-polluting energy sources, EVs have a significant life cycle emissions advantage over conventional gasoline or diesel vehicles.
Additionally, EVs are more energy-efficient than gasoline vehicles, using approximately 87-91% of battery energy for propulsion, compared to gasoline vehicles' 16-25% energy conversion rate. While EV manufacturing may have higher emissions due to battery production, this is improving with evolving technology, and batteries produced using renewable energy have lower lifetime emissions.
Overall, EVs typically have lower total GHG emissions associated with their manufacturing, charging, and operation than gasoline vehicles, making them a viable option for reducing emissions, especially in regions with cleaner electricity generation.
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The aviation sector is hard to decarbonise
The transportation sector is one of the largest contributors to US greenhouse gas emissions. In 2022, it accounted for the largest portion (28%) of total US greenhouse gas emissions.
The aviation industry contributes to roughly 2.5% of global carbon emissions, with combustion of jet fuel being one of the most important mechanisms by which it contributes to climate change. Despite the relatively smaller contribution, the aviation sector is hard to decarbonize due to several reasons.
Firstly, the unique power and energy requirements of air travel, coupled with weight and size constraints, make electrification extremely difficult. Energy-dense fossil fuels are currently the most cost-effective way to meet these requirements. Additionally, key technologies such as Sustainable Aviation Fuels (SAFs) are relatively costly and have not been adopted at scale.
Secondly, the aviation sector has long innovation cycles and prioritizes safe operations, which can slow down the implementation of new technologies. Furthermore, the sector is highly interdependent, with actors such as commercial aviation lessors, OEMs, and suppliers all needing to work together to support airlines and offer solutions.
Finally, the aviation sector faces competition from other industries such as marine and road transport, which are sourcing from the same sustainable fuel feedstock. This affects the balance of SAF supply and demand and, therefore, its market price.
Overall, while the aviation sector is committed to reducing its climate footprint, it faces several challenges and obstacles that make it difficult to decarbonize.
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Frequently asked questions
Transportation is responsible for about 28% of total US carbon emissions, making it the largest contributor. Cars, trucks, commercial aircraft, and railroads are some of the sources of these emissions.
Walking or cycling for short to medium distances is the lowest-carbon way to travel. For longer distances, trains are a good alternative. Using a train instead of a car for medium-length distances can reduce emissions by around 80%. Electric vehicles are also a good alternative to petrol or diesel cars.
There are several approaches to reducing carbon emissions from transportation. These include low-carbon fuels, improved vehicle technologies, strategies to reduce vehicle miles traveled, and operating vehicles more efficiently. For example, the EPA's SmartWay program helps freight transportation companies improve supply chain efficiency and reduce greenhouse gas emissions.
