Environmental Assessment of Bus Transport in the Trondheim Region - Evaluation of Relevant Bus and Fuel Technologies and their Potential for Mitigating Emissions from Passenger Transportation

摘要

The overall aim of this thesis is to assess the carbon footprint of transport by bus in the Trondheim region. Bus transportation is promoted as a strategy both to combat local pollution problems in urban areas and to mitigate global greenhouse gas emissions from passenger transport. Still, the environmental impacts of bus transport have received fairly limited attention in research. The environmental impacts of bus transport are calculated through life cycle assessment. A model is developed for the bus and fuel technologies included in the bus fleet in Trondheim. The analysis is limited to city buses, which in Trondheim comprise hybrid, natural gas and biodiesel buses. All life cycle phases of bus transport are included. The environmental impacts are measured by the impact categories climate change, fossil depletion, eutrophication, acidification, particulate matter formation and land occupation. The thesis draws on previous LCA studies of cars to compare GHG emissions per passenger kilometer between different bus routes. A comparison is also made for work travels in Trondheim to investigate the effect of climate mitigation measures implemented the later years. The results shows that the hybrid bus performs best in terms of greenhouse gas emissions and fossil depletion per vehicle kilometer, while the natural gas bus had lower emissions in the remaining five impact categories. By switching to biogas, it is found that this bus technology achieved similar impacts to the hybrid bus also in the two former categories. Looking at specific bus routes, it is found that buses with 5-10 passengers had lower GHG emissions than a car with 1-2 persons, depending on the bus technology. Both technology advancements and modal shifts are promoted by national authorities as ways to reduce the overall emissions from passenger transportation. Comparing the carbon footprint of work travels between 2009 and 2014 shows that the modal shift had the largest mitigation effect.The largest reduction potential per vehicle kilometer is identified in the operation phase of the buses. With the use of biofuels, these emissions can be reduced significantly. The mitigation potential is however dependent on the type of biofuels, thus policy makers should be aware of problem shifting.