The majority of trucks that run on liquefied natural gas emit about the same amount of greenhouse gases as diesel trucks.
Felipe Rodríguez is programme lead at ICCT
Cross posted from the ICCT website
Trucks running on liquefied natural gas (LNG) continue to be promoted by the truck and gas lobbies as a bridge technology for decarbonizing the road freight sector. A newly released study I drafted with Öko-Institut debunks this notion. Moreover, our findings lead to a worrying conclusion: LNG trucks provide little-to-no climate benefit. Still, they enjoy substantial regulatory and fiscal incentives that can put the decarbonization of road freight transport on a bridge to nowhere.
The logic used to lobby for LNG-friendly policies—ranging from higher targets for LNG filling stations to exempting LNG-trucks from road-tolls—is easy to follow: 1) natural gas has a significantly lower carbon content than diesel for the same energy content, 2) gas trucks emit fewer air pollutants than diesel, and 3) truck and infrastructure investments can be leveraged in the transition to full decarbonization through the use of bio- or synthetic-methane. Let’s dissect those one at a time.
With its roughly 25% lower carbon content than diesel and its decent energy density, LNG does have some appeal as an alternative fuel for long-haul trucks. However, issues quickly become apparent when assessing not only CO2 but all greenhouse gas (GHG) emissions across the complete well-to-wheel (WTW) fuel chain. The figure below shows the WTW performance of diesel and LNG-trucks, in equivalent grams of CO2 per kilometer, using two time periods to estimate the climate impacts, 20 and 100 years. Focusing on the 100-year timeframe, the WTW greenhouse gas performance of LNG trucks equipped with spark-ignited (SI) engines is only 2% better than that of diesel-powered trucks. Spark ignition is the most common technology for LNG engines; Scania and Iveco both use this combustion concept. The WTW GHG emissions of LNG trucks equipped with more efficient high-pressure direct injection (HPDI) engines, newly introduced by Volvo, are only approximately 9% lower than diesel. In the 20-year timeframe, which illustrates more immediate climate risks, LNG trucks are invariably worse than diesel, due to the strong short-term climate impact of methane. So, looking at the whole WTW picture, the advantage of the lower carbon content of methane evaporates as quickly as venting LNG.
As far as air pollutant emissions are concerned, the prevailing notion that natural gas engines are cleaner than diesel is no longer valid in the current technology landscape. Advances in diesel emission control systems, new combustion concepts for natural gas engines such as HPDI, and a better understanding of ultrafine particulate emissions of unfiltered SI engines challenge the established narrative that natural gas engines produce fewer pollutant emissions than diesel. Technology improvements in emission control systems, such as better thermal management of the aftertreatment or the addition of particle filters to SI engines, have the potential to further reduce the pollutant emissions of both diesel and LNG engines. When it comes to the air quality impact of diesel and LNG trucks, there is no clear advantage of one over the other.
The final common argument in favor of LNG-trucks is that Europe’s gas supply can be transformed into a fully renewable resource in the coming decades. This is nothing but wishful thinking. Biogas will only deliver GHG benefits if it is produced from low-carbon feedstocks, such as wastes and sustainable residues. The problem is that there is just not enough cow manure, garbage, and agricultural waste to meet demand. While power-to-gas does not have the same feedstock limitations, it does face other economic constraints. Furthermore, powering a truck with power-to-gas is much less efficient than using the same renewable electricity to power a fuel cell or battery-electric truck. Combined, biogas and power-to-gas could meet at most 12% of the EU’s projected total gas demand in 2050 at a very high cost to taxpayers, as it would require huge policy support.
Yes, LNG trucks can deliver a paltry climate benefit. However, the technology can lock the European Union on a pathway that is not compatible with its climate-neutrality goals. Hence, the regulatory and fiscal incentives that LNG trucks enjoy today should be revisited.
As the above figure shows, GHG emissions of LNG trucks are systematically underestimated in the European CO2 regulations for trucks, as a large portion of tank-to-wheel emissions are not considered. For example, the current certification procedure neglects methane and nitrous oxide emissions. The emissions of these two powerful climate pollutants can be addressed by implementing separate GHG standards for engines, including correction factors in the simulation tool used for certification (i.e., VECTO), enforcing strict not-to-exceed limits as part of Euro VII, or, better yet, by a combination of these measures.
In addition to receiving an unwarranted regulatory advantage, LNG trucks are promoted in some EU member states through fiscal incentives. In Germany, LNG trucks are subsidized at purchase, exempt from road-tolls, and pay over 70% less fuel energy tax than diesel trucks. These subsidies amount to over €70,000 in the first five years of vehicle use. Given the limited GHG benefit of LNG trucks over diesel—2% for SI-LNG and 9% for HPDI-LNG—this is a very inefficient subsidy scheme, costing taxpayers up to €7,000 per tonne of CO2 saved. For comparison, the penalties set by the truck CO2 standards in 2025 translate to around €250 per tonne of CO2. Clearly, an extension of subsidies for LNG trucks, such as the recommendation by the Transport Committee of the German Bundestag to extend the road-toll exemption, is groundless.
LNG trucks are an expensive technology, the promotion of which is at odds with the European Union’s goal of CO2-neutrality by mid-century. Policymakers would be wise to stop the inefficient incentives and subsidies for this futile technology. Likewise, manufacturers should follow in the steps of the world’s largest truck maker, Daimler, and end their R&D activities in LNG and instead concentrate on the development of fuel cell and battery electric trucks.