Environmental impact of underground freight transport

The transport sector has a large share in many environmental problems. Several new transport systems, including various forms of underground freight transport, have been proposed to reduce the environmental impact. However, literature on the life-cycle and environmental impact of such systems is very scarce, reason enough to focus this paper on the assessment of the energy use of and resulting emissions from transport systems, in which the emphasis will be on underground freight transport systems. Evaluation of the energy use and its environmental effects necessitates a complete as possible analysis of the energy use, both directly and indirectly arising from the transport process. Direct energy use is the energy necessary for actually moving the passengers or goods, in most cases the energy used by transporting vehicles. Indirect energy use results from processes like the building and maintenance of infrastructure and vehicles. Whereas direct energy use is typically calculated by sophisticated models, methods for the analysis of indirect energy use are much less developed. This paper will examine one of these methods, the process energy analysis, along with the process emission analysis, which is the process energy analysis equivalent for calculating indirect emissions of greenhouse gases (CO₂), acidifying gases (SO₂, NO_x) and other air-polluting substances (VOC, PM₁₀). The total lifetime energy use and emissions are estimated using these methods in two case studies. In the first case, transport of crude oil by Dutch long-distance pipelines is evaluated, while the concern in the second case is the so-called Underground Logistic System (ULS) Utrecht concept for the underground distribution of packed goods in the city of Utrecht. This is an innovative concept that makes use of automatic guided vehicles. Each case revealed very distinct characteristics related to the proportion of direct versus indirect energy use and emission levels. Crude oil pipelines have, typically, low direct energy intensities and emission factors, and also very low indirect energy use and emissions compared to other transport modes. Contrarily, the ULS Utrecht is characterised by low direct energy and emission intensities. However, the high indirect energy use and emissions require very high transport intensities to result in a net reduction compared to the alternatives: road transport in most cases. Furthermore, the 44relationship between direct and indirect emissions of different substances is highly variable.