Well-to-wheel greenhouse gas emissions comparison of electricity and biomethane urban buses

Public transport can represent an important solution to reduce the greenhouse gas emissions of the transport sector, even more when relying on low-carbon powertrains. Compared with other public transport modes that are already mostly electrified, buses still rely on oil products in many cities around the world. This work analyses two promising alternative options for urban mobility, by evaluating the greenhouse gas emissions intensity of the supply chains of battery electric buses and biomethane-powered internal combustion engines. In addition to general results, the analysis also presents a focus on each EU country, to highlight the potential variability related to different operating conditions. The outcome of the study confirms that interesting emissions savings can be achieved through the substitution of diesel buses with these low-carbon alternatives. The level of emissions savings depends on the source of electricity generation and the feedstock used to produce biomethane. A bus fleet composed by half electricity and half biomethane buses could lead to savings between 70%–125% depending on the country (figures higher than 100% can be obtained thanks to negative emissions associated to biomethane production from some feedstocks). These results can support decision makers working on strategies to reduce emissions of urban transport modes, as they confirm the interesting opportunity represented by these technologies compared to the current situation, and even more when considering them against the use of private cars in urban environments.