Understanding the contribution of tunnels to the overall energy consumption of and carbon emissions from a railway

Tunnels can contribute significantly to the overall energy consumption and carbon emissions of a railway, both in terms of embodied energy and emissions (those associated with the materials and the construction process) and in terms of operational energy and emissions (due to the increased air resistance experienced by a train inside a tunnel). Although tunnels may be a necessary component of railway infrastructure, it is important that their impact on carbon emissions is fully understood, especially when comparing the railway with other modes. This paper reviews existing literature and uses a case study to develop understanding. Trade-offs between embodied and operational energy and emissions are explored.