Table of Contents
Introduction
Biofuels play an important role in reducing fossil fuel use in road transport, especially where internal combustion engine vehicles still dominate. In this chapter the focus is on how biofuels are used in road transport, what types exist, how they perform in practice, and which sustainability questions they raise. Broader topics such as overall transport emissions or other renewable transport options are treated elsewhere, so they are only touched here when needed for context.
What Are Biofuels In Road Transport?
Biofuels for road transport are liquid or gaseous fuels produced from biological material, usually called biomass. They are designed to replace or blend with conventional gasoline and diesel in cars, trucks, and buses. The key idea is that the carbon released when biofuels are burned was originally absorbed from the atmosphere by plants during growth, so biofuels can, under the right conditions, contribute to lower net greenhouse gas emissions compared with fossil fuels that release carbon long stored underground.
For road transport, the most relevant biofuels today are ethanol and biodiesel, along with their more advanced variants. Biogas and other gaseous fuels also exist but are less common in private cars and are more often used in specific fleets or regions.
Main Types Of Biofuels For Road Transport
Ethanol And Gasoline Blends
Fuel ethanol is an alcohol produced by fermenting sugars or starches from crops such as sugarcane, corn, wheat, or from cellulosic materials such as crop residues and grasses. In road transport it is almost always used blended with gasoline.
Common blends include E5 and E10, where the number indicates the percentage of ethanol by volume. E5 contains 5 percent ethanol and 95 percent gasoline, E10 contains 10 percent ethanol and 90 percent gasoline. Many countries have made E5 or E10 the standard gasoline at filling stations. In some places higher blends such as E15 or E20 exist, usually for newer vehicles that have been tested and approved for such concentrations.
There are also high ethanol blends such as E85, with up to 85 percent ethanol. These require flexible fuel vehicles that are specifically designed or calibrated to run on high ethanol content as well as pure gasoline. Ethanol has a lower energy content per liter than gasoline. As a result, vehicles running on high ethanol blends usually consume more fuel by volume to travel the same distance, even if energy efficiency can be similar.
Feedstocks for ethanol matter for sustainability. Ethanol from sugarcane often has relatively favorable greenhouse gas performance due to high yields and use of residues for energy, while ethanol from some food crops in certain farming systems can be more controversial. Advanced or cellulosic ethanol, produced from non food parts of plants or from residues, aims to reduce these concerns.
Biodiesel, FAME, And HVO
For compression ignition engines that normally use diesel, biodiesel is the most common biofuel. Conventional biodiesel in many markets is fatty acid methyl ester, often abbreviated as FAME. It is produced by transesterification of vegetable oils or animal fats such as rapeseed oil, soybean oil, used cooking oil, or tallow with methanol. This process produces biodiesel and glycerin as a byproduct.
Blends of biodiesel with fossil diesel are designated similarly to ethanol blends. For example B5 contains 5 percent biodiesel and 95 percent fossil diesel, B20 contains 20 percent biodiesel. Many diesel vehicles can operate on low blends such as B7 without modification. Higher blends or pure biodiesel, called B100, usually require engine and fuel system compatibility checks and can affect maintenance schedules, particularly in cold climates where biodiesel can gel at higher temperatures than fossil diesel.
A newer category is hydrotreated vegetable oil, often abbreviated HVO, or more broadly hydroprocessed esters and fatty acids. These fuels are produced by reacting oils or fats with hydrogen, and the resulting fuel has properties very similar to fossil diesel. HVO can often be used in existing diesel engines at higher blend levels or even as a drop in fuel, subject to engine manufacturer approval. Because of its better cold flow performance and stability, HVO is increasingly used for trucks, buses, and fleet vehicles where higher biofuel content is required.
Biogas And Biomethane For Vehicles
Although less common in private cars, biogas and its upgraded form, biomethane, are relevant for buses, refuse trucks, and some regional fleets. Biogas is produced from anaerobic digestion of organic waste such as food waste, manure, and sewage. When cleaned and upgraded to biomethane, its quality becomes similar to fossil natural gas and it can be injected into gas grids or used as a vehicle fuel in compressed or liquefied form.
In road transport biomethane is mainly used in compressed form in vehicles designed for compressed natural gas. From the user perspective such vehicles refuel at specific gas filling stations. While the infrastructure requirements are different from liquids like gasoline and diesel, biomethane allows organic waste streams to be turned into useful vehicle fuel and can deliver significant greenhouse gas reductions, especially when methane emissions from waste would otherwise be high.
How Biofuels Are Used In Practice
Low Blend Biofuels As The Current Mainstream
Across many countries the most widespread use of biofuels in road transport is through low blends that can be used in the existing vehicle fleet. Ethanol blended into gasoline at up to 10 percent by volume and biodiesel blended into diesel at up to 7 percent are common regulatory targets. Fuel suppliers are often required by law to include a minimum share of renewable content in their fuels. For drivers this often happens without any change in vehicle behavior and sometimes without them even noticing, since the fuel is sold at standard pumps.
These low blends are attractive for policy makers because they provide a relatively straightforward way to reduce average greenhouse gas intensity of fuels, at least on paper, while avoiding the need to replace millions of vehicles or dramatically change refueling infrastructure. However, the actual climate benefit depends strongly on the production pathway and agricultural practices used for the feedstocks.
High Blends And Dedicated Fleets
High blends such as E85 for ethanol or B20 and above for biodiesel are mainly found in specific markets or fleets that can manage compatibility and supply. For example, taxi fleets, delivery trucks, or bus operators may commit to using higher blend fuels under contracts with fuel suppliers. These users can adapt maintenance schedules, ensure that engines are certified for the fuels used, and centralize refueling at their own depots.
Flexible fuel vehicles for high ethanol blends have been especially common in Brazil, where E85 and even higher sugarcane ethanol blends are widely available and where vehicle designs and standards evolved around that reality. Some European countries use high biodiesel blends in buses, sometimes with specific winter and summer fuel formulations to manage cold flow issues.
Biomethane and other gaseous biofuels also follow this pattern, with dedicated fleets that use specific refueling stations. Public transport agencies and waste collection services often pioneer such approaches because they can coordinate vehicles, refueling infrastructure, and procurement contracts over many years.
Drop In Biofuels And Long Term Compatibility
A key technical challenge for biofuels is whether they can be used as drop in fuels. This means that the fuel can fully replace its fossil counterpart in any existing vehicle system without modification. Most mainstream biofuels today are blends that displace part of the fossil fuel. However, advanced biofuels such as HVO have properties that are closer to fossil diesel and in some cases can be used at 100 percent concentration in compatible engines.
Drop in biofuels are particularly attractive for heavy duty vehicles, where batteries are still challenging for some long distance applications, and for long lived assets that cannot be easily electrified. While this chapter focuses on road transport, similar issues arise in other sectors. For road vehicles, drop in capability can reduce barriers for adoption and improve the potential for higher renewable shares without changing engines or refueling hardware.
Climate And Environmental Performance In Road Use
Tailpipe Versus Life Cycle Emissions
From a vehicle exhaust pipe perspective, burning biofuels releases carbon dioxide and in some cases slightly different profiles of other pollutants compared with fossil fuels. However, the climate impact of biofuels is not determined by tailpipe emissions alone. It depends on the entire life cycle, including cultivation or collection of biomass, processing into fuel, distribution, and final combustion.
In life cycle assessment, a simplified energy balance for a fossil gasoline vehicle can be expressed as:
$$
E_{\text{total}} = E_{\text{well to tank}} + E_{\text{tank to wheel}}
$$
where $E_{\text{total}}$ is the total energy related to fuel use, $E_{\text{well to tank}}$ is energy used in extraction, refining, and transport, and $E_{\text{tank to wheel}}$ is the energy released during combustion in the vehicle. For biofuels, a similar concept applies, but the upstream part includes agricultural operations, processing, and sometimes land use change.
The greenhouse gas savings of a biofuel compared to a fossil reference are often expressed as a percentage reduction in life cycle emissions per unit of delivered energy. Regulations frequently set minimum thresholds that biofuels must meet in order to count toward renewable targets or receive incentives.
When evaluating biofuels, it is essential to use full life cycle greenhouse gas emissions, not just tailpipe emissions, to judge climate benefits.
Land Use Change And Indirect Effects
One of the most debated aspects of biofuels in road transport is land use change. When forests, wetlands, or grasslands are converted to grow biofuel crops, large amounts of carbon can be released from soils and biomass. This can offset, or in extreme cases exceed, the emissions savings from replacing fossil fuels for many years.
Indirect land use change is even more complex. If existing food production is displaced by biofuel crops, it can push agricultural expansion into new areas elsewhere. These effects are difficult to measure accurately but have led to concerns that some conventional, crop based biofuels may not deliver the expected climate benefits.
Because of these risks, many policy frameworks now distinguish between conventional biofuels from food and feed crops and advanced biofuels from non food biomass such as residues, wastes, or dedicated crops grown on marginal lands. Caps on conventional biofuels, sustainability criteria, and incentives for advanced pathways aim to shift the sector in a more sustainable direction.
Air Pollution And Engine Performance
At the local level, biofuels can affect air pollutant emissions such as particulate matter, nitrogen oxides, carbon monoxide, and unburned hydrocarbons. The effects are not uniform and depend on the blend level, engine type, and emission control technologies.
Ethanol blends generally reduce carbon monoxide and some hydrocarbon emissions, but can increase evaporative emissions and some aldehydes. Biodiesel blends often reduce particulate matter and carbon monoxide, but can increase nitrogen oxides in some engine configurations. Modern engines with advanced after treatment systems are designed to meet emission standards on a range of fuels, and differences between fuels can be modest in these cases.
In many cities, the combined use of cleaner engines, filters, and appropriate fuel quality specifications is more important for local air quality than the difference between low percentage biofuel blends and pure fossil fuels. However, high blends without suitable engine optimization can cause issues such as injector deposits, filter clogging, or unburned fuel, which can indirectly affect emissions and reliability.
First Generation Versus Advanced Biofuels In Road Transport
Conventional Or First Generation Biofuels
First generation biofuels are produced from food or feed crops that have been used traditionally for food markets. Examples include corn ethanol, sugarcane ethanol, and biodiesel from rapeseed or soybean oil. These fuels were the first to be deployed at large scale because the conversion technologies are relatively simple and well known.
In road transport, first generation biofuels still make up a significant share of biofuel volumes in many regions, especially where agricultural sectors are strong and there are policy incentives to support farmers. However, concerns about competition with food production, land use change, and biodiversity loss have led to debates about how far this pathway should expand.
Advanced Biofuels And Their Promise
Advanced biofuels are produced from non food biomass such as agricultural residues, forestry residues, organic waste, or dedicated energy crops that can be grown on marginal land. They include cellulosic ethanol, biomass to liquid diesel, biogas and biomethane from wastes, and HVO produced from used cooking oil and other waste fats.
For road transport, advanced biofuels can deliver higher greenhouse gas savings per unit of fuel and reduce pressure on agricultural land if managed well. They can also contribute to waste management by using streams that would otherwise emit methane or require disposal. However, their production technologies have often been more complex and expensive, and commercial scale deployment has been slower than initially hoped.
In recent years, the most successful advanced biofuel routes in road transport have been those that build on available waste oils and fats for HVO and those that use biogas from waste streams. These options are attractive because they combine energy production with waste treatment and avoid direct competition with food crops.
Policy And Market Drivers For Biofuels In Road Transport
Blending Mandates And Fuel Standards
Most large scale use of biofuels in road transport is driven by policy. Blending mandates require fuel suppliers to include a minimum percentage of biofuel in the total volume of gasoline or diesel that they sell. Alternatively, some systems allow suppliers to meet a greenhouse gas intensity target through a combination of biofuels and other measures.
Fuel quality standards define what blends are acceptable for general use. For example, they specify maximum percentages of ethanol or biodiesel in standard fuels, set limits on properties such as water content, acidity, or stability, and align with vehicle manufacturers' warranties. These standards ensure that fuels sold at public pumps are safe for the majority of vehicles on the road.
Sometimes policy makers introduce different categories of biofuels with specific treatment. Waste and residue based fuels may receive extra credit in renewable fuel standards, allowing suppliers to meet their obligations with smaller physical volumes if they use fuels with higher greenhouse gas savings.
Support Mechanisms And Trade
In addition to mandates, governments may support biofuels through tax reductions, direct subsidies, or capital grants for production plants. At the same time, biofuels are traded internationally, especially ethanol and biodiesel, which raises questions about how sustainability criteria are applied across borders.
For road transport this trade means that a liter of fuel purchased at a filling station may be part of a global supply chain that starts with crops or waste in a very different region of the world. Sustainability certification schemes aim to verify that producers meet certain environmental and social standards, but their effectiveness depends on enforcement and transparency.
Role Of Biofuels In A Changing Road Transport System
Complementing Electrification
As road transport moves toward greater electrification, especially for cars and light duty vehicles, the role of biofuels will also evolve. In segments where battery electric vehicles can cover most needs, such as urban passenger cars, the demand for gasoline and diesel, and thus for blended biofuels, may decline.
However, for heavy duty trucks, long distance freight, and some specialized vehicles, electrification can be more difficult in the short to medium term. In these segments, high quality biofuels that can be used in existing diesel engines may remain important as a transitional or complementary solution. They can help achieve emission reductions in parts of the fleet that are slow to electrify fully.
Legacy Vehicle Fleets And Transition
Even with ambitious policies for electrification, many combustion engine vehicles will remain on the road for years. Biofuels provide one of the few options to lower emissions from this existing fleet without replacing vehicles. This is particularly relevant in regions where the average vehicle age is high or where incomes limit the uptake of new technologies.
The long term outlook for biofuels in road transport will therefore depend on the pace of vehicle turnover, the speed of electric vehicle adoption, the development of alternative fuels in other sectors, and societal choices about land, food, and ecosystems. In a sustainable scenario, biofuels are likely to be used more selectively, focusing on routes that deliver high greenhouse gas savings, use waste and residues, and target the most challenging vehicle segments.
Key Takeaways For Beginners
Biofuels in road transport are a diverse group of fuels that can be blended into gasoline and diesel or used in dedicated vehicles, and they are already present in everyday fuels in many countries. Their climate benefit is not automatic, but depends on how and from what they are produced, with life cycle emissions, land use, and feedstock type all playing a critical role.
In the current transition, biofuels act as a bridge solution for existing vehicles and difficult to electrify segments, while advanced pathways based on wastes and residues offer the most promising long term potential. Understanding these basic distinctions helps to interpret policy debates, fuel labels at the pump, and claims about green fuels in road transport.