Renewable fuels may deliver fastest emissions cuts for Europe’s freight sector

Europe’s climate ambitions face a major obstacle in the freight transport sector, where millions of diesel-powered trucks continue to operate across long-distance logistics networks. While governments have introduced ambitious decarbonization targets, replacing the entire heavy-duty vehicle fleet with zero-emission alternatives remains a slow and complex process due to infrastructure costs, technological barriers, and the long lifespan of commercial vehicles.

To iron this out, researchers are examining alternative fuels that could reduce emissions from the vehicles already on the road. The study “Decarbonization of EU Road Freight Transport in the Short and Medium Term Through Renewable Liquid Fuels—A Review,” published in the journal Energies, evaluates renewable diesel options such as biodiesel and hydrotreated vegetable oil as near-term tools for lowering transport emissions.

The fossil fuel challenge in European freight transport

The European Union’s road transport system remains heavily dependent on fossil fuels despite growing investments in clean mobility. Transport is the largest final energy consumer across EU sectors and relies overwhelmingly on oil-based fuels. Diesel alone accounts for the majority of energy consumption in road transport, reflecting the dominant role of diesel-powered trucks, buses, and commercial vehicles.

The composition and age of the vehicle fleet further complicate decarbonization efforts. Millions of passenger cars, light commercial vehicles, and heavy-duty trucks currently operate across the EU, many of them more than a decade old. Heavy-duty commercial vehicles in particular have an average age exceeding fourteen years, making them the oldest segment of the transport fleet.

These older vehicles are almost entirely powered by fossil fuels. Diesel dominates the sector, with only a very small fraction of heavy-duty vehicles using alternative propulsion technologies such as electricity or hybrid systems. Because of the high purchase cost of new vehicles and the long operational life of freight trucks, replacing the entire fleet with zero-emission vehicles would take decades even under aggressive policy scenarios.

This slow turnover means that a large number of diesel trucks will remain on European roads for many years. According to the study, this reality creates a major policy dilemma. While electrification and hydrogen technologies are essential for long-term decarbonization, immediate emissions reductions must also address the vehicles already in operation. Renewable liquid fuels therefore emerge as one of the few solutions capable of delivering short- and medium-term carbon reductions without replacing engines or building entirely new fuel distribution systems.

European policymakers have already introduced several climate strategies to address the transport sector. Initiatives such as the European Green Deal, the Sustainable and Smart Mobility Strategy, and the Renewable Energy Directive set ambitious targets for reducing greenhouse gas emissions and increasing renewable energy use in transport. These frameworks aim to dramatically lower emissions by 2030 and achieve climate neutrality by mid-century. However, reaching these goals will require both long-term technological transformation and near-term mitigation measures.

Biodiesel and renewable diesel as transitional solutions

Among renewable fuel options, the study focuses on two fuels that can directly substitute conventional diesel: biodiesel and hydrotreated vegetable oil. Both fuels can be produced from renewable biological resources and can be used in existing diesel engines, making them practical candidates for rapid deployment.

Biodiesel, commonly referred to as fatty acid methyl ester fuel, is produced through the chemical transesterification of vegetable oils, animal fats, or recycled cooking oils. During this process, triglycerides react with alcohol in the presence of a catalyst to produce methyl esters that can serve as a renewable diesel substitute.

One of biodiesel’s most significant advantages is its potential to reduce lifecycle greenhouse gas emissions. Because biodiesel is derived from biological feedstocks that absorb carbon dioxide during growth, its overall carbon footprint can be significantly lower than that of fossil diesel. Lifecycle analyses indicate that biodiesel can reduce carbon dioxide emissions by substantial margins when compared with petroleum-based fuels.

Biodiesel also contains oxygen in its molecular structure, which improves combustion efficiency in diesel engines. This characteristic can reduce emissions of particulate matter, carbon monoxide, and unburned hydrocarbons. These improvements contribute to cleaner exhaust profiles and may also help address urban air pollution.

However, biodiesel is not without drawbacks. The fuel has a slightly lower energy content than conventional diesel, meaning vehicles may require greater fuel volumes to achieve the same energy output. Biodiesel also has higher viscosity and can exhibit poor cold-flow properties, which may cause operational challenges in colder climates.

The study also highlights concerns related to engine durability. Long-term use of biodiesel can lead to issues such as injector deposits, fuel filter clogging, lubricant dilution, and wear of sealing materials within fuel injection systems. Although many diesel engines can operate with biodiesel blends, these technical limitations can restrict the percentage of biodiesel used in fuel mixtures.

Hydrotreated vegetable oil represents another renewable diesel alternative with several distinct advantages. Unlike biodiesel, which contains oxygenated molecules, HVO is produced through a hydrogenation process that converts biological oils and fats into paraffinic hydrocarbons similar to those found in fossil diesel. This chemical structure allows HVO to function as a near-direct replacement for conventional diesel.

Because of its composition, HVO exhibits several favorable fuel properties. It typically has a higher cetane number than diesel, which enhances ignition quality and combustion efficiency. The fuel also offers improved stability during storage and better performance in cold conditions compared with biodiesel.

HVO can be used in existing diesel engines without major mechanical modifications, and many commercial vehicle manufacturers have approved its use across a wide range of truck models. This compatibility makes it particularly attractive as a drop-in renewable fuel that can be integrated into current fuel infrastructure.

Engine studies show that HVO can reduce several types of tailpipe emissions, including carbon monoxide, hydrocarbons, and particulate matter. Some research also indicates modest reductions in carbon dioxide emissions compared with fossil diesel. However, the effects on nitrogen oxide emissions remain uncertain, with different studies reporting varying outcomes depending on engine design and operating conditions.

Another limitation is cost. The hydrogen-intensive production process required for HVO can make it more expensive than both conventional diesel and biodiesel. As a result, large-scale adoption may depend on supportive policies, incentives, and technological improvements in production efficiency.

Role of fuel blends in future decarbonization

The study suggests that combining biodiesel and HVO may represent a promising pathway for optimizing renewable diesel performance. Blended fuels can potentially balance the strengths and weaknesses of each component while maintaining compatibility with existing engines and distribution systems.

For example, biodiesel can improve the lubricity of fuel blends, helping reduce friction and wear in fuel injection systems. HVO, on the other hand, provides greater chemical stability and improved cold-weather performance. When combined, these fuels may produce a balanced mixture that retains environmental benefits while minimizing operational drawbacks.

Research into biodiesel and HVO blends is still emerging, and the available data remain limited. Some studies suggest that blending biodiesel with HVO can improve certain fuel properties without significantly reducing energy density. At the same time, increasing biodiesel content in such blends may lead to higher nitrogen oxide emissions under certain conditions.

Because of these uncertainties, the authors emphasize the need for additional research into the performance, emissions, and long-term reliability of blended renewable fuels in diesel engines. Improved understanding of these interactions could help optimize fuel formulations for specific vehicle types and operating conditions.

To sum up, the findings suggest that the path toward cleaner freight transport will likely involve multiple technologies operating simultaneously. Renewable liquid fuels could provide a practical bridge between today’s diesel-dominated transport system and the future of electrified and hydrogen-powered logistics.