Green transportation

The transportation sector is emitting more and more CO2 from cars, trucks, airplanes and shipping. To reverse this trend, more of the known solutions and technologies need to come into play.

Metro on bridge in a green area near Ørestad, Copenhagen
The transition to green transportation is making its mark in Denmark with more electric cars, electric charging stations, special parking spaces, and for aviation, a political agreement has been reached that all domestic aviation must be converted to green energy by 2030.
 
Electric cars have a positive effect on CO2 emissions, but the energy efficiency they create has been exchanged for longer trips. The latest Transport Habits Survey from DTU shows that Danes are driving the same number of trips in their cars, but they are making longer trips. As a result, CO2 emissions from driving are as high as they were 30 years ago.
 
Overall, the transport sector, including cars, trucks, airplanes and domestic shipping, accounts for 25 percent of total CO2 emissions in Denmark, which amounted to 44 million tons of CO2 in 2022. The transition to sustainable transportation is therefore central to Denmark reducing CO2 emissions by 70% by 2030.
 
The government's expert group behind a report on green tax reform has presented models for how taxes can reduce agricultural CO2 emissions. If one of the models is implemented, the transportation sector will be the largest emitter of CO2. Increased research and development in areas such as electrification, development of green fuels, battery technology and optimization of logistics in the freight and maritime sectors play a key role in the green transition.

FAQ about green transportation

See our answers to the most common questions about green transportation.

In addition to cycling and walking, green transportation includes modes of transport that run, fly or sail on fuels other than fossil fuels, such as gasoline and diesel. By replacing fossil fuels, electrified or green transportation helps reduce the overall environmental impact by emitting less CO2 and other pollutants.

Currently, most transportation companies, shipping companies and airlines rely on fossil fuels such as gasoline and diesel for transportation.

If CO2 emissions are to be reduced, the transportation sector plays a significant role. Passenger and goods transport accounts for 25% of total CO2 emissions in Denmark, which amounted to 44 million tons of CO2 equivalents in 2022.

According to the report of an expert group for a green tax reform  (Svarer-udvalget) set up by the government, the transport sector is expected to be responsible for 39% of Danish CO2 emissions in 2030. The transportation sector is therefore central to Denmark's goal of a 70% overall reduction in emissions by 2030.

The most sustainable mode of transportation is still cycling and walking or transporting people and goods around the world using green power. Unlike biofuels, for example, green power can be scaled sustainably. However, wind and solar power are associated with periods of non-production when the wind doesn't blow and the sun doesn't shine, and both forms of energy require the expansion of the electricity infrastructure.

Electrification has a particularly large potential in road transportation, i.e. so that all cars, vans and trucks run primarily on electric batteries. In addition, the electric engine is significantly more energy efficient than an internal combustion engine and therefore consumes less energy in the form of electricity than an equivalent car or truck running on fossil fuels.

The EU has set the framework for switching to electricity in road transportation by ensuring charging infrastructure throughout Europe and setting CO2 requirements for new vehicles.

Passenger cars account for around 60% of CO2 emissions from the transport sector in the EU, according to figures from the European Environment Agency, EEA in 2022. With an average of 1.4 people per car in Denmark in 2022, car sharing or switching to public transport, cycling or walking can help reduce emissions.

According to the European Environment Agency, CO2 emissions from cars can be reduced by making vehicles more efficient, using different fuels or electric cars. Although most cars in Europe use gasoline, electric cars are increasingly gaining ground. Electric cars still have a small market share of total car sales in the EU, with 10 million new electric cars sold in 2023, representing a market share of 14.6%.

Green fuels are often referred to as e-fuels or electro-fuels because they are made using electricity from wind turbines and solar cells. The fuels are produced through electrolysis, where water molecules (H20) are split into hydrogen (H2) and oxygen (O). Electrolysis requires a large energy input in the form of electricity.

Hydrogen can be used directly as a fuel, or it can be used in a synthesis process where nitrogen (N) or carbon (C) from CO2 is added. This creates new fuels and chemicals such as ammonia, methanol and methane. They can be used as fuels for ships, planes and trucks, or as fertilizer in agriculture. Research is being conducted into combining the two processes so that power-to-x can be done more simply and efficiently in a single, unified process that uses the electricity to directly produce an x other than hydrogen. This could be e-methanol or e-kerosene, which can be used as fuel in heavy transportation.

However, the efficiency of this form of energy is very low, equivalent to about 20% of the electricity used to produce the fuel, so it is a very expensive form of energy.

Read more about DTU's work on power-to-X

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Professor at DTU Physics Jakob Kibsgaard explains what Power-to-X is and why Power-to-X is an essential element in the green transition.
Professor at DTU Physics Jakob Kibsgaard explains what Power-to-X is and why Power-to-X is an essential element in the green transition.

Passenger cars are one of the biggest polluters, accounting for 60.6% of total CO2 emissions from road transportation in Europe. Therefore, if emissions are to be reduced, it is crucial that car emissions are brought down by making cars run longer on electricity or other fuels. In terms of influencing the consumption of fossil fuels, DTU professor Jeppe Rich believes that taxes on gasoline and diesel directly at the pump will have the greatest impact. 

With an average of 1.6 people per car in Europe in 2018, switching to public transportation can help reduce emissions.

According to the Danish Ministry of Climate, Energy and Utilities, electrification of road transportation by switching to electric cars and trucks is the most mature and market-ready technology.

For sectors that may be more difficult to electrify, such as parts of aviation and shipping, green fuels such as biofuels and electro fuels may be an option, but they are expensive to produce.

According to a transport and environmental study published by the European Environment Agency (EEA) in 2021, rail travel is still the most environmentally friendly form of motorized passenger transport in Europe in terms of greenhouse gas emissions compared to car or air travel.

The report looks specifically at the impacts of rail and air travel, both of which make up a large part of Europe's passenger transport sector and concludes that rail travel is the best and most sensible mode of transport, apart from walking and cycling.

Measured by the number of kilometers traveled by each passenger, emissions from aviation are significantly higher. However, the report points out that traveling by plane is not necessarily the most harmful choice. Emissions can be higher if you drive alone in a gasoline or diesel car.

The sustainability of electric cars can be measured by how far they can drive on electricity produced from renewable energy sources and how much raw materials and energy are used to manufacture their batteries, among other things.

From a lifecycle perspective, electric cars are currently described as low-emission cars, but the expectation is that electric cars will eventually become zero-emission cars. This requires battery technology to be based on more sustainable raw materials that can be extracted and produced with less energy consumption. 

In a 2018 analysis, the Danish Council on Climate Change reviewed a number of studies comparing CO2 emissions from different car types over the entire lifetime of the car. Based on this, the Council concludes that even though there is no CO2 coming out of the tailpipe, from a lifecycle perspective, the electric car today is a low-emission car, not a zero-emission car.

Most studies show that the electric car is more climate-friendly than the fossil alternative, and the electric car will become even more climate-friendly as electricity production is increasingly based on renewable energy.

Global shipping accounts for between 2% and 3% of global energy-related CO2 emissions.

Shipping is facing increasing pressure to reduce its climate footprint. The industry has committed to reducing CO2 by 50% by 2050. At the same rate, world trade and thus shipping is expected to increase.

Methanol or ammonia as a fuel can pave the way to reach these ambitious goals. Ammonia does not contain carbon and therefore does not produce CO2.

DTU Professor Peter Glarborg is currently investigating how ammonia burns if it is supplemented with hydrogen as a support fuel. If hydrogen is based on green electricity, it will be a CO2-neutral fuel. Neither ammonia nor methanol are great fuels.

They both require a supporting fuel to ensure ignition, so technology development is required. Researchers at DTU are working to develop new injectors, which are a key element if alternative fuels are to work in practice.

Green aviation fuel is similar to jet fuel that is currently approved for use in aircraft. The difference is that in the future, the fuel will be produced from green raw materials and not from fossil crude oil.

Just like in the production of other green fuels for heavy traffic, jet fuel can be produced by using electricity from wind turbines or solar cells to split hydrogen from water through electrolysis. By further processing the hydrogen in a synthesis process with CO2, fuels such as methanol or e-kerosene, electronic kerosene, can be produced that have the potential to reduce the climate impact of aviation.

Contact our experts in green transportation

Transportation

Ninette Pilegaard

Ninette Pilegaard Deputy Head of Division, Head of Section

Section Manager and Division Manager Ninette Pilegaard is an expert in the development of traffic and the challenges of the transition to green transportation - including which instruments promote the transition to electric cars and transportation with low CO2 emissions.

Energy systems

Jacob Østergaard

Jacob Østergaard Professor, Head of Division

Professor Jacob Østergaard is one of Denmark's leading researchers in future energy systems. He is an expert in energy islands and has in-depth knowledge of both their potential and challenges. Jacob Østergaard has worked intensively with the integration of electric cars into the energy system and has used Bornholm as a living laboratory for electrification for more than 15 years.

Green Fuels

Henrik Lund Frandsen

Henrik Lund Frandsen Professor

Henrik Lund Frandsen research Power-to-X, i.e. the conversion of green electricity into different fuels, with a special focus on electrolysis technologies and their integration in plants to produce green hydrogen for methanol, aviation fuel and ammonia.

Become an engineer and make a difference

Several of DTU's study programmes provide skills and knowledge that you can use to make a difference within green transportation.

See all DTU’s study programmes
Researcher prepares and isolates fuel cells and electrolysis cells for testing in DTU Energy's test laboratory at DTU Risø Campus.

The history of green transportation and DTU

Some of the first cars were powered by batteries, but gasoline cars quickly took over the market. However, as the link between climate change and greenhouse gas emissions were demonstrated, green technology moved up the transportation agenda.

Follow the development through some historical reference points involving DTU and Denmark.

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