Investigating the environmental sustainability of rail travel in comparison with other modes

Abstract

Sustainability is a broad concept which embodies social, economic and environmental concerns, including the possible consequences of greenhouse gas (GHG) emissions and climate change, and related means of mitigation and adaptation. The reduction of energy consumption and emissions are key objectives which need to be achieved if some of these concerns are to be addressed. As well as being an important component of sustainability in other sectors, a good transport system needs to be sustainable in its own right. Energy consumption and GHG emissions are important issues within the transport sector; in the European Union (EU), for example, transport is directly responsible for between 25 and 30 percent of all carbon dioxide (CO2) emissions, and the inclusion of indirect (Scope 2 and Scope 3) GHG emissions may increase this proportion further. If reduction targets are to be met, it may be necessary to encourage behavioural change, including modal shift from those modes of transport which are comparatively highly polluting, towards those modes which pollute less. Rail is potentially a suitable target for such modal shift from road transport (notably the private car for passenger travel) and, in some case, from short-haul and domestic aviation. However, modal comparisons are often based on average data, and are reliant on a number of assumptions. There are likely to be some circumstances where modal shift towards rail makes more sense than others, but the use of average data does not enable policy makers to be discerning. It should also be noted that many modal comparisons are also based purely on operational energy consumption and emissions, and neglect to take the whole life-cycle in to account. Embedded energy and emissions from the construction of vehicles and infrastructure can be quite significant, as can the energy consumption and emissions from vehicle idling in the case of public transport modes. After considering the concept of environmental sustainability, this research begins by reviewing existing energy consumption and emissions data for vehicle operation, where it is noted that data for cars in Europe are quite comprehensive. Manufacturers are obliged to publish fuel consumption and emissions data for each model of car they sell, although the type approval tests do not reflect real-world performance. Studies are reviewed which suggest that the gap between the tests and the real-world has been widening in recent years. The gap appears to be independent of the size of vehicle, but is larger for hybrid vehicles than it is for those powered solely by a petrol or diesel internal combustion engine. Data for trains are less comprehensive, and that data which are available are often based on a limited empirical sample, or simulated data for which a number of assumptions have been made. Sometimes, the details of the measurements taken or simulation parameters used are unclear. As a result, published data for a particular type of train in the literature are sometimes found to vary significantly. In order to make more informed comparisons between rail and other modes, two large empirical datasets have been analysed. Two UK Train Operating Companies (TOCs) have also made data from energy metering systems on-board their electric trains available, which have been used to analyse the actual energy consumption of different trains over a number of different routes. The sample size is far larger than that found in literature to date, and it has been possible to consider variation between routes and service types. The basic principles of simulating the energy consumption (and related emissions) of a train have also been illustrated, and a software tool has been developed for Arup so that it can now make some estimate of operational energy consumption and emissions for a given train over a given route. The aforementioned empirical data have also been used to validate the tool and suggest some appropriate simulation parameters. A review of existing literature concerning whole life-cycle analysis has been undertaken. It is clear that life-cycle costs vary significantly but in general, the overall life-cycle costs of rail appear to be higher than those for any other mode. The biggest additional factors appear to be the embedded carbon and energy in the infrastructure, particularly for a system comprising a lot of bridges, tunnels and large underground stations. For the vehicles themselves, trains typically have a longer lifespan than cars, which reduces the embedded carbon and energy as functions of time. When comparisons are made between modes, passenger-km is a metric which is often chosen, because it helps account for some of the fundamental differences between modes, including the fact that public transport modes usually use vehicles which are much bigger than the private car. In order to make comparisons on this basis, however, something about the load factor must be known. The sensitivity to load factor is demonstrated, and the earlier empirical data analysis is used to illustrate the benefits of longer trains. A discussion then follows about the potential pitfalls of making comparisons purely on a per passenger-km basis. This thesis ends by summarising some of the findings. Some consideration is given towards the future and the fact that technological developments are being made in Sustainability is a broad concept which embodies social, economic and environmental concerns, including the possible consequences of greenhouse gas (GHG) emissions and climate change, and related means of mitigation and adaptation. The reduction of energy consumption and emissions are key objectives which need to be achieved if some of these concerns are to be addressed. As well as being an important component of sustainability in other sectors, a good transport system needs to be sustainable in its own right. Energy consumption and GHG emissions are important issues within the transport sector; in the European Union (EU), for example, transport is directly responsible for between 25 and 30 percent of all carbon dioxide (CO2) emissions, and the inclusion of indirect (Scope 2 and Scope 3) GHG emissions may increase this proportion further. If reduction targets are to be met, it may be necessary to encourage behavioural change, including modal shift from those modes of transport which are comparatively highly polluting, towards those modes which pollute less. Rail is potentially a suitable target for such modal shift from road transport (notably the private car for passenger travel) and, in some case, from short-haul and domestic aviation. However, modal comparisons are often based on average data, and are reliant on a number of assumptions. There are likely to be some circumstances where modal shift towards rail makes more sense than others, but the use of average data does not enable policy makers to be discerning. It should also be noted that many modal comparisons are also based purely on operational energy consumption and emissions, and neglect to take the whole life-cycle in to account. Embedded energy and emissions from the construction of vehicles and infrastructure can be quite significant, as can the energy consumption and emissions from vehicle idling in the case of public transport modes. After considering the concept of environmental sustainability, this research begins by reviewing existing energy consumption and emissions data for vehicle operation, where it is noted that data for cars in Europe are quite comprehensive. Manufacturers are obliged to publish fuel consumption and emissions data for each model of car they sell, although the type approval tests do not reflect real-world performance. Studies are reviewed which suggest that the gap between the tests and the real-world has been widening in recent years. The gap appears to be independent of the size of vehicle, but is larger for hybrid vehicles than it is for those powered solely by a petrol or diesel internal combustion engine. Data for trains are less comprehensive, and that data which are available are often based on a limited empirical sample, or simulated data for which a number of assumptions have been made. Sometimes, the details of the measurements taken or simulation parameters used are unclear. As a result, published data for a particular type of train in the literature are sometimes found to vary significantly. In order to make more informed comparisons between rail and other modes, two large empirical datasets have been analysed. Two UK Train Operating Companies (TOCs) have also made data from energy metering systems on-board their electric trains available, which have been used to analyse the actual energy consumption of different trains over a number of different routes. The sample size is far larger than that found in literature to date, and it has been possible to consider variation between routes and service types. The basic principles of simulating the energy consumption (and related emissions) of a train have also been illustrated, and a software tool has been developed for Arup so that it can now make some estimate of operational energy consumption and emissions for a given train over a given route. The aforementioned empirical data have also been used to validate the tool and suggest some appropriate simulation parameters. A review of existing literature concerning whole life cycle analysis has been undertaken. It is clear that life-cycle costs vary significantly but in general, the overall life-cycle costs of rail appear to be higher than those for any other mode. The biggest additional factors appear to be the embedded carbon and energy in the infrastructure, particularly for a system comprising a lot of bridges, tunnels and large underground stations. For the vehicles themselves, trains typically have a longer lifespan than cars, which reduces the embedded carbon and energy as functions of time. When comparisons are made between modes, passenger-km is a metric which is often chosen, because it helps account for some of the fundamental differences between modes, including the fact that public transport modes usually use vehicles which are much bigger than the private car. In order to make comparisons on this basis, however, something about the load factor must be known. The sensitivity to load factor is demonstrated, and the earlier empirical data analysis is used to illustrate the benefits of longer trains. A discussion then follows about the potential pitfalls of making comparisons purely on a per passenger-km basis. This thesis ends by summarising some of the findings. Some consideration is given towards the future and the fact that technological developments are being made in both the motor and the rail industries.both the motor and the rail industries.

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ORCID for J.M. Preston: orcid.org/0000-0002-6866-049X

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