Systematic Review and Bibliometric Analysis of Approaches to Improving Energy Efficiency and Reducing Emissions in Transport

Energy use in transport and the associated emissions remain major challenges for the transition towards sustainable mobility and freight systems. This study provides a systematic and bibliometric review of approaches to improving energy efficiency and reducing emissions across different modes of transport. Records retrieved from Scopus up to 12 September 2026 were screened in accordance with the PRISMA 2020 framework and analysed using bibliometric mapping and structured content analysis. Of the 2885 records initially identified, 2300 formed the bibliometric corpus and 510 studies were included in the final structured analysis. The bibliometric analysis identified five major thematic clusters and revealed a rapid expansion in research activity, particularly after 2020. Road transport accounted for 71.6 percent of the analytical corpus, whilst electrification and alternative fuels constituted the dominant intervention category (45.9 per cent). Energy and emission outcomes were reported in 66.9 per cent and 66.1 per cent of studies, respectively, but only 33.1 per cent evaluated both dimensions jointly. The evidence base was strongly model-oriented: optimisation, simulation/modelling, scenario/system dynamics, and LCA/WTW accounted for 85.5% of studies, whereas directly measured evidence accounted for only 4.5%. Digital technologies were identified in 54.3% of studies and AI/data-driven methods in 39.6%. The findings indicate an increasing integration of propulsion technologies, energy management, operational optimisation and digital methods, whilst highlighting the need for stronger real-world validation, more comparable energy and emission metrics, and broader evidence across under-represented modes of transport.