Effects of alignment on CO2 emissions from the construction and use phases of highway infrastructure
Hughes, Lynsay Anne
University of Cambridge
Department of Engineering
Doctor of Philosophy (PhD)
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Hughes, L. A. (2013). Effects of alignment on CO2 emissions from the construction and use phases of highway infrastructure (Doctoral thesis). https://doi.org/10.17863/CAM.11735
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The environmental aspect of sustainability is currently high on many agendas due at least in part to the issue of climate change, manifesting in the monitoring of C02 emissions from all activities within all industrial sectors, with construction projects being no exception. The concept of Whole Life Carbon (WLC) involves understanding the carbon impact of an infrastructure project from its beginning, through its serviceable life, to the end of its life. The WLC concept can be applied to future infrastructure projects to assist in decision making, to ensure the correct project is taken forward in terms of minimising carbon emissions across the life time of the infrastructure. The life cycle of a highway project comprises the planning, design, construction, operation, use and decommissioning phases. For a new 23km motorway project in the UK, when considering the construction and use phases, the C02 emissions from vehicles using the road comprised 91% over a 40 year period. With the majority of C02 resulting from the use phase, any measures taken to minimise the impacts of this could potentially significantly reduce the C02 over the lifetime of a highway. It is during the planning stage that decisions can be made to reduce the WLC; by forecasting the impact of different design options at the different future phases of the life cycle. This thesis considers the effect of highway alignment, which is a decision taken early in a project's life cycle. The gradient of a highway can have a significant impact on the fuel consumption (and hence C02 emissions) of the vehicles operating on it. To design the alignment around an optimum earthworks phase in terms of time, cost and carbon may result in a construction phase with a lower impact, yet the long term effect of the subsequent gradients on vehicle fuel consumption may yield a significantly higher level of C02 emissions than the amount saved during the efficient construction operation. Conversely, an intensive earthworks operation may result in a C02 intensive construction phase yet result in long term benefits throughout the life cycle, as the fuel consumed by the vehicles operating on the highway is reduced. To understand the effect of the vertical alignment through the life cycle, the C02 in both the construction and use phases has been calculated. A methodology to calculate the C02 from the earthworks operations has been developed. The instantaneous emission model, PHEM, has been used to calculate the C02 from the vehicles using a highway. Different vehicle types have been assessed over hypothetical terrains, with the application of varying fleet mixes and vehicle speeds enabling an understanding of the effect of alignment on typical vehicle flows. These alignments have been modified, requiring more C02 intensive earthworks operations, to understand the potential benefits the new alignment can bring to the use phase, and the overall life cycle. The methodology developed has been applied to an actual case study that had six very different horizontal and vertical alignments. A second real and current project was used to gain an understanding of the C02 impacts of choosing an embankment over a viaduct structure.
This record's DOI: https://doi.org/10.17863/CAM.11735