Sustainable transport refers to transportation that minimizes harm to the environment and society. To evaluate sustainability, factors such as the type of vehicles used, the energy source, and the infrastructure (like streets, railways, airways, waterways, and canals) are considered. Transport sustainability is measured by how well a system works, how efficiently it uses resources, and its effects on the environment and climate. Transport systems have a major impact on the environment. In 2018, transportation was responsible for about 20% of global carbon dioxide emissions. Greenhouse gas emissions from transport are rising faster than in any other sector that uses energy. A 2023 study in the Journal of Transport Geography found that shared electric bicycle systems reduce urban carbon emissions by about 108–120 grams per kilometer, especially in non-central urban areas and when powered by low-carbon electricity. Road transport also contributes significantly to local air pollution and smog.

Sustainable transport systems benefit the environment, society, and economy of the communities they serve. These systems connect people to jobs, education, and services, and low-income households often benefit from affordable, low-carbon transport options. The benefits of increased mobility must be balanced with the environmental, social, and economic costs of transport systems. Short-term efforts often focus on improving fuel efficiency and reducing vehicle emissions. Long-term goals include replacing fossil fuel-based energy with renewable energy sources. Every stage of a transport system’s life is evaluated for sustainability.

The United Nations Environment Programme (UNEP) estimates that avoiding outdoor air pollution could prevent about 2.4 million premature deaths each year. Black carbon, a type of fine particle in the air, is especially harmful. It causes respiratory and cancer-related diseases and contributes to climate change. Lowering carbon emissions through sustainable transport reduces climate change risks and improves public health by enhancing air quality. The term "green mobility" describes clean and sustainable ways of moving people or goods.

Transport systems also have social costs, such as traffic accidents, air pollution, lack of physical activity, time spent commuting, and dependence on fuel prices. Traffic congestion costs money by wasting time and slowing the delivery of goods and services. Traditional planning often focuses on vehicle mobility without considering broader impacts. However, the true purpose of transport is to provide access to work, education, services, and social connections. Techniques exist to improve access while reducing environmental and social harm and managing traffic. Cities that improve transport sustainability often do so as part of larger efforts to create livable, sustainable communities.

Definition

The term "sustainable transport" became widely used as a natural next step after the idea of sustainable development. It refers to ways of moving people and goods, and how transportation systems are planned, that align with broader goals of sustainability. There are many ways to define sustainable transport and related terms like "sustainable transportation" and "sustainable mobility." One definition, from the European Union Council of Ministers of Transport, describes a sustainable transportation system as one that:

• Ensures people, businesses, and society can meet their needs safely, while protecting human and ecosystem health and ensuring fairness for future generations.
• Is affordable, runs fairly and efficiently, offers different transportation choices, supports a strong economy, and helps regions grow in a balanced way.
• Reduces pollution and waste to levels the Earth can handle, uses renewable resources without exceeding their natural supply, and uses non-renewable resources only as much as renewable alternatives can replace them, while reducing land use and noise.

Sustainability is not just about how efficiently something works or how much pollution it creates. A life-cycle assessment looks at the entire journey of a product—from making it, using it, to what happens after it's no longer needed. A cradle-to-cradle design, which considers the whole life of a product, is more important than focusing on just one part, like energy efficiency.

Benefits

Sustainable transport provides many social and economic benefits that can help speed up local sustainable development. According to important studies by the Low Emission Development Strategies Global Partnership (LEDS GP), sustainable transport can create jobs, improve safety for people traveling by investing in bicycle lanes, pedestrian paths, and other types of paths. It also makes access to jobs and social activities more affordable and efficient. Additionally, it helps save time, reduce household expenses, and lower government costs, making investment in sustainable transport a "win-win" opportunity.

Environmental impact

Transport systems are a major source of greenhouse gas emissions. In 2004, transportation was responsible for 23% of global energy-related greenhouse gas emissions, with about three-quarters coming from road vehicles. By 2011, transportation was linked to one-third of all greenhouse gases produced. Today, 95% of transport energy comes from petroleum. Energy is used in making vehicles, using them, and building transport infrastructure like roads, bridges, and railways. Motorized transport also releases harmful exhaust fumes, including particulate matter that harms human health and contributes to climate change.

The first attempts to study the environmental impact of vehicles over their entire life cycle were made by Theodore Von Karman. For many years, improvements focused on refining his model. Later, Dewulf and Van Langenhove created a new model based on energy use and efficiency principles. Chester and Orwath developed a similar model that considers the costs of building infrastructure.

Transportation’s environmental impact can be reduced by making vehicles lighter, promoting energy-efficient driving, reducing tire friction, encouraging electric and hybrid vehicles, improving walking and cycling conditions in cities, and expanding public transport, especially electric rail systems.

A 2006 study by Lawrence D. Frank and others showed that increasing walkability by 5% led to benefits such as a 6.5% drop in vehicle miles driven, a 5.6% reduction in nitrogen oxide emissions, and a 5.5% decrease in volatile organic compound emissions.

Green vehicles aim to have less environmental impact than standard vehicles. However, their overall impact depends on factors like the energy used in manufacturing and the electricity source.

Electric vehicles significantly reduce carbon dioxide emissions compared to traditional gasoline-powered vehicles. The extent of this reduction depends on the energy used in manufacturing the vehicle and the electricity source. Even in countries with high coal use, like China and India, electric vehicles still produce fewer emissions. For example, a Nissan Leaf in the UK in 2019 produced one-third of the greenhouse gases of a typical gasoline-powered car.

The Online Electric Vehicle (OLEV), developed by Korea Advanced Institute of Science and Technology (KAIST), is an electric bus that can charge while moving or stopped, eliminating the need to stop at charging stations. In South Korea’s Gumi City, a 24 km route allows the bus to receive 100 kW of electricity at 85% efficiency while maintaining a 17 cm gap between the vehicle and the road. Only small sections of the road need embedded cables for this system. Hybrid vehicles, which combine internal combustion engines with electric engines, are already widely used.

Natural gas is sometimes used as a transport fuel, but it remains a fossil fuel with significant emissions, though lower than gasoline or diesel.

In 2007, Brazil met 17% of its transport fuel needs with bioethanol. However, the OECD noted that Brazil’s success with first-generation biofuels depends on local conditions. Globally, first-generation biofuels are expected to have little impact on emissions at a high cost. Later generations of biofuels (second to fourth) offer better environmental benefits, as they avoid deforestation and reduce conflicts between food and fuel production.

In practice, the environmental impact of transport depends on the sustainability of the chosen method. Green vehicles use less fuel than standard vehicles but still contribute to traffic and accidents. Public transport systems, such as diesel buses, use less fuel per passenger than private vehicles and are generally safer and take up less road space. Green public transport, like electric trains, trams, and buses, combines efficiency with sustainability. Human-powered transport, such as cycling, and animal-powered transport also have very low environmental impact. Walking is the most environmentally friendly transport choice. Rail transport is highly efficient.

Transport and social sustainability

Cities with too many roads have faced unexpected problems, including big decreases in public transportation, walking, and biking. In many areas, streets became less lively. Businesses, schools, government buildings, and libraries moved away from city centers, and people who stayed in cities had less access to good public spaces and services. When schools closed, larger schools in suburbs caused more traffic; the number of cars on US roads between 7:15 and 8:15 a.m. increased by 30% during the school year.

Another issue was more people leading inactive lifestyles, which worsened a national problem of obesity and led to higher healthcare costs.

Car-focused transportation systems create challenges for low-income neighborhoods, as many people in these areas must use cars they cannot afford to keep, making it harder to earn a living. This situation is called "forced car ownership."

These effects are not the same for everyone, creating differences in how transportation works across different communities, known as a "transport divide."

Potential shift to sustainable transport in developing countries

In countries like Uganda, researchers have studied factors that might influence people to choose bicycles instead of motorcycle taxis (boda boda). The results show that a person's age, gender, and ability to ride a bicycle are important factors that affect their decision to use bicycles. Improving transportation systems to make cycling safer was also found to be a major way to increase bicycle use.

Cities

Cities are shaped by how people move within them. In The City in History, Lewis Mumford wrote about how cities were often built around a walkable center, usually near a port or waterway. Suburbs were connected to the city through animal transport, later by rail or tram lines.

In 1939, the New York World’s Fair showed a model of a city designed for cars. This imagined city had separate areas for homes, businesses, and factories, with tall buildings over roads. These ideas influenced city planning from the 1940s to the 1970s.

After World War II, the rise of cars changed how cities were built. Some people opposed these changes. Jane Jacobs, in The Death and Life of Great American Cities, described the loss of community life during this time. Lewis Mumford asked, “Is the city for cars or for people?” Donald Appleyard studied how car traffic affected neighborhoods in The View from the Road (1964). In the UK, Mayer Hillman researched how traffic impacted children’s ability to move freely in 1971. Despite these concerns, car use and fuel use increased rapidly after the war.

In Europe, transport planning has not always focused on private cars. For example, the Dutch Transport Structure Scheme, since the 1970s, requires that new road projects only be approved if they benefit society. Since 1990, it has aimed to cut the growth of car traffic in half. Cities like Curitiba, Brazil; Portland, Oregon; and Vancouver, Canada, have linked transport planning to sustainability and land use.

Cities use different amounts of energy for transport. On average, a person in the U.S. uses 24 times more energy for private cars than someone in China, and almost four times more than someone in Europe. These differences are not only due to wealth but also to how much people walk, bike, or use public transport, as well as city design and density.

Cities that focused heavily on car-based systems are now the least environmentally friendly, as measured by fossil fuel use. Car-based systems have also been questioned for their long-term social and economic effects. In the U.S., people in sprawling cities drive more and farther than those in traditional neighborhoods. New York City residents save about $19 billion yearly by owning fewer cars and driving less. Carsharing, where people rent cars instead of owning them, is growing in North America and Europe. It is estimated that one shared car can replace 15 owned cars. Carsharing is also expanding in developing countries, where traffic and crowding are often worse. Companies like Zoom in India, eHi in China, and Carrot in Mexico are helping reduce pollution and improve access to cars.

In 2009, the European Commission created the Action Plan on urban mobility to support sustainable transport. It reviewed progress in 2012 and considered future steps. In 2007, 72% of Europeans lived in cities, which are vital for jobs and growth. Efficient transport systems help cities support their economy and people. About 85% of the EU’s GDP comes from cities. Urban areas must make transport sustainable by reducing pollution, traffic, and noise while addressing social needs like health, mobility for people with disabilities, and family needs.

The C40 Cities Climate Leadership Group includes 94 cities worldwide working to cut greenhouse gas emissions and improve urban life. In 2019, 35 mayors signed the C40 Clean Air Cities Declaration, agreeing that clean air is a human right. Studies using satellite data show that cities with subway systems produce less greenhouse gas.

Bogotá, Colombia, has a key example of sustainable transport: the TransMilenio Bus Rapid Transit (BRT) system. Launched in 2000, this system became a global model for efficient public transport. It carries up to 43,000–48,000 passengers per hour on its busiest routes. Buses use special lanes to avoid traffic, and passengers pay before boarding to speed up entry. Large buses are used to carry many people at once.

Bogotá also has one of the world’s largest cycling networks, with over 560 kilometers of bike lanes. The city promotes non-motorized travel through events like Ciclovia, which opens streets to cyclists and pedestrians on certain days.

Policies and governance

In 2008, the UK Government passed the Climate Change Act, which required a reduction of 80% in greenhouse gas emissions by 2050, compared to levels in 1990. In 2019, the law was updated to require a 100% reduction in emissions by 2050, meaning the UK aims to reach a net zero target, where no more greenhouse gases are added to the atmosphere than are removed.

In 2021, the UK Department for Transport released a plan called "Decarbonising Transport. A better, greener Britain." This plan explains how the UK transport sector will reduce carbon emissions by 2050. The plan focuses on six main goals: shifting people to walking, cycling, and public transport; reducing emissions from cars and trucks; improving freight transport; supporting new technologies; creating solutions tailored to local areas; and reducing emissions from planes and ships.

In 2021, the Institute for Public Policy Research stated that car use in the UK must decrease, and more people should use walking, cycling, and public transport. The Department for Transport responded by saying they will spend 2 billion pounds on improving walking and cycling paths, as well as making railways greener. Studies in the UK show that switching from flying to taking the train could reduce CO₂ emissions by 60 times.

Some Western countries are working to make transportation more sustainable in both short-term and long-term plans. For example, Freiburg, Germany, has improved public transport, cycling, and walking, and created areas where cars are not allowed.

In many Western countries, people rely heavily on personal vehicles for travel, with about 80% of trips made by car. This makes cars one of the largest sources of greenhouse gas emissions in the United States. To reduce emissions, the federal government must create plans that include improving public transport by expanding coverage, using new technology to make public transport more reliable, and encouraging walking and biking by building wider sidewalks, bike-sharing stations, and limiting parking near shopping areas. Other steps include increasing parking fees and tolls to raise the cost of car ownership and gas prices, which may encourage people to use more fuel-efficient vehicles. However, this could create fairness issues because lower-income people often drive older, less efficient cars. The government can use money from taxes and tolls to improve public transport and help poor communities.

Other countries and states have used research from behavioral economics to create policies that promote sustainable transportation.

In March 2022, France will require all car advertisements to include a message promoting sustainable transport, such as walking, cycling, or using public transport. This rule applies to all vehicles, including electric cars. By 2028, it will be illegal to advertise cars that produce more than 128 grams of carbon dioxide per kilometer.

Sustainable transport policies have the most impact at the city level.

In Western Europe, some large cities have made progress in sustainable transport. In Paris, 53% of trips are made by walking, 3% by bicycle, 34% by public transport, and 10% by car. In the Ile-de-France region, walking is the most common way to travel. In Amsterdam, 28% of trips are by walking, 31% by bicycle, 18% by public transport, and 23% by car. In Copenhagen, 62% of people use bicycles to commute to school or work.

Outside Western Europe, cities like Curitiba, Brazil; Bogota, Colombia; Portland, Oregon; and Vancouver, Canada, have included sustainability in their transport and land use planning. In 2010, the state of Victoria, Australia, passed the Transport Integration Act, which requires transport agencies to consider sustainability, including climate change, in their planning.

Many cities worldwide have joined the Cities for Climate Protection program to link sustainability with transport policies. Some cities are working to become car-free by limiting or banning car use.

In 2020, the COVID-19 pandemic led some cities, such as Milan, London, Brighton, and Dublin, to increase biking and walking to support social distancing and reduce traffic congestion and air pollution. Similar plans were adopted by New York City and Paris. However, the pandemic also reduced revenue for public transport, which may force governments to provide financial support to transport operators, potentially limiting funds for greener projects.

Sustainable transport is a movement that began with environmental concerns but has grown to include efforts to ensure fairness and access for all people, including those with lower incomes and mobility challenges. Many people who face the most noise, pollution, and safety risks from cars are those who cannot afford or do not own cars.

An organization called Greenxc, started in 2011, encouraged people in the United States to carpool by sharing rides across the country and documenting their journeys. Carpooling reduces carbon emissions by allowing multiple people to share one car instead of driving individually.

A study by Prospect Sierra Students showed that changing transportation habits could reduce school-related carbon emissions by 15.5%. Their research found that 50% of drivers live within a 2-mile walk of school, 30% are within a carpool range, and 30% are within a 2-5 mile carpool range.

At the start of the 21st century, some companies began using sailing ships for commercial purposes, such as Fairtrannsport and New Dawn Traders, who created the Sail Cargo Alliance.

The European Investment Bank committed €314 million between 2018 and 2022 to support green marine transport, including building new ships and upgrading existing ones with eco-friendly technology. The bank also provided an average of €11 billion per year from 2012 to 2022 for sustainable transport and climate-friendly projects. In 2022, railway projects received about 32% of transport loans, and urban mobility projects received about 37%.

Recent trends

Car travel increased steadily during the twentieth century, but trends since 2000 have become more complicated. Rising oil prices starting in 2003 are connected to a decrease in the amount of fuel used per person for private vehicle travel in the United States, Britain, and Australia. In 2008, global oil use dropped by 0.8% overall, with large decreases in North America, Western Europe, and parts of Asia.

Other reasons for reduced driving in America include the retirement of Baby Boomers, who now drive less, younger people choosing other travel options like public transportation, the effects of the Great Recession, and the growing use of technology (such as the internet and mobile devices), which have made travel less necessary or appealing.

The term "green transport" is often used in marketing to describe products that are not proven to help the environment. These claims can be legally challenged. For example, the Norwegian Consumer Ombudsman has taken action against car companies that use terms like "green," "clean," or "environmentally friendly." Companies may face fines if they do not stop using these words. The Australian Competition & Consumer Commission (ACCC) says that "green" claims on products are unclear and can mislead consumers. In 2008, the ACCC required a car retailer to stop promoting Saab cars as "green," as the Australian Federal Court found the marketing to be misleading.

According to the International Energy Agency (IEA), the transportation sector causes more than one-third of global CO₂ emissions. This trend has led to the development of technologies and practices that reduce transportation’s environmental impact, such as electric and hydrogen-powered vehicles, autonomous systems, smart mobility platforms, and energy-efficient infrastructure. Patenting activity shows where innovation is happening. Between 2000 and 2020, the number of published patent families related to transportation increased from about 11,000 to nearly 120,000.

Sustainable propulsion is a key area for reducing transportation’s environmental impact. Research and patents focus on batteries, efficient aircraft turbines, efficient ship designs, electric propulsion, hydrogen fuel cells, and sustainable fuels.

Automation and circularity aim to improve production efficiency, reduce waste, and increase recycling.

Communication and security technologies help create safer, more connected transportation systems that respond to changing conditions. These include innovations like lidar sensors, 5G networks, connected vehicles, smart city infrastructure, and smart ports.

Between 2000 and 2023, sustainable propulsion and communication and security technologies saw the largest increase in patent publications. Sustainable propulsion is the most patented technology in land and sea transport, while communication and security technologies account for over 85% of patents in space transport.

Tools and incentives

Several European countries are offering financial support to encourage more environmentally friendly ways of traveling. The European Cyclists' Federation, which works to promote daily cycling for transportation, has created a document that includes an incomplete summary of these efforts. In the UK, employers have long provided financial support to employees. Employees can lease or borrow bikes that their employers purchase. Additional support may also be available. This program helps employees save money and encourages them to include physical activity in their daily routines. Employers may benefit by reducing taxes, decreasing sick days, and reducing the need for car parking spaces. Since 2010, Iceland has had a program called Samgöngugreiðslur. Employees who do not drive a car to work receive a monthly payment. To qualify, employees must agree to use a car for work no more than once a week or 20% of the time during a period. Some employers pay fixed amounts based on trust, while others reimburse expenses for bicycle repairs, public transport tickets, and similar costs. Since 2013, payments up to ISK 8,000 per month have been tax-free. Most major workplaces offer this program, and many employees use it. Since 2019, half of the payment is tax-free if the employee agrees to use a car for work less than 40% of the time during the contract period.

The EU Directorate-General for Transport and Energy (DG-TREN) has started a program focused on improving urban transportation. Key parts of the program include:

• Clean fuels and vehicles: Animal-powered transport, biodiesel, biogas/CNG, electric vehicles, human-powered transport, hybrid vehicles, hydrogen vehicles, LPG, sailing ships
• Sustainable (green) transport infrastructure: Bikeways, busways, greenways, foreshoreways, railways
• Access restrictions: Access management, car-restricted zones, living streets, multifunctional areas, parking management, pedestrian zones, traffic calming/speed reduction
• Integrated pricing strategies: Congestion pricing, integrated ticketing, parking management
• Collective passenger transport: Accessible transport systems, bus rapid transit, bus services, demand-responsive transport, integrated ticketing, intercity bus service, intermodal transfers, marketing, paratransit, park-and-ride, public transport, quality of service, rail transport, security (including transit police)
• Travel information: Public transport route planners (intermodal journey planner)
• Less car-intensive lifestyle: Bike sharing, car pooling, car sharing, car/driver license exit strategies, cycling
• Soft measures: Travel blending, travel plans, personalized travel plans, walking school bus
• Transport management: New urbanism and New Pedestrianism, TDM Toolbox, transit-oriented development, transportation demand management, walkability
• Sustainable freight transport: Clean vehicles/clean fleet, dry port, fleet management, intermodal freight transport, route planning, transportation management system

History

Most of the tools and ideas used in sustainable transport were created before the term was first used. Walking, the first way people traveled, is also the most sustainable method. Public transportation began at least as early as when Blaise Pascal invented the public bus in 1662. The first passenger tram started operating in 1807, and the first passenger train service began in 1825. Pedal bicycles were first used in the 1860s. These were the main personal transportation choices for most people in Western countries before World War II. Today, these same options are still the main choices for many people in developing countries. Freight, or goods being moved, was transported using human power, animal power, or rail before other methods were developed.

After World War II, more wealth and a greater need for movement of people and goods led to changes. In Britain, the number of road vehicles increased five times between 1950 and 1979, with similar trends in other Western countries. Wealthier nations and cities invested heavily in building larger and better roads and highways, which were seen as important for growth and prosperity. Transport planning became part of urban planning, and planners began to focus on "induced demand," which showed that building more roads could lead to more traffic, shifting from the old idea of "predict and provide" to a more sustainable approach that included planning land use and improving public transit. Public funding for transit, walking, and cycling dropped sharply in the United States, Great Britain, and Australia, though this did not happen as much in Canada or mainland Europe.

Concerns about the long-term effects of this approach grew during the 1973 oil crisis and the 1979 energy crisis. High fuel costs and limited fuel supplies led to renewed interest in alternatives to driving alone.

Transport innovations from this time include high-occupancy vehicle lanes, citywide carpool systems, and transportation demand management. Singapore was the first country to use congestion pricing in 1975, and Curitiba started its Bus Rapid Transit system in the early 1980s.

Low and steady oil prices in the 1980s and 1990s led to a large increase in vehicle travel between 1980 and 2000. This happened both because people chose to drive more often and for longer distances and because cities built large areas of suburban housing far from workplaces and shops, now called urban sprawl. Changes in freight logistics, such as moving from rail and coastal shipping to road transport and the need for quick deliveries, caused freight traffic to grow faster than general vehicle traffic.

At the same time, the ideas behind the "predict and provide" approach to transport planning were questioned, especially by Peter Newman, who studied cities and their transport systems in the mid-1980s.

The British Government’s White Paper on Transport marked a change in how transport planning was done in the UK. In the introduction, Prime Minister Tony Blair stated that

A report called "Smarter Choices," which accompanied the White Paper, studied ways to expand small sustainable transport projects in Britain. It found that using these methods widely could reduce car traffic during busy times in cities by more than 20%.

A similar study by the United States Federal Highway Administration, released in 2004, also concluded that taking a more active approach to managing transportation demand was an important part of the country’s overall transport strategy.

Mobility transition refers to the process of changing how people and goods move to more sustainable methods using renewable energy. It includes combining different types of private and public transportation, changing how public spaces are used, and finding new ways to fund and plan cities. The main goal is to reduce harm from traffic, such as accidents and damage to the environment, and to make cities more livable. It also aims to solve problems related to logistics, social needs, economic issues, and energy use.

Transport changed many times during the 19th and 20th centuries. Canal boats, steam railways, and bicycles replaced walking and horse-drawn travel. Steamships replaced sailing ships. Later, these were replaced by vehicles powered by internal combustion engines and, in some cases, electricity. These were then partly replaced by cars and airplanes.