Effect of alignment on life cycle C02 emissions of highway infrastructure

The life cycle of an infrastructure project comprises the planning, design, construction, operation, use and decommissioning phases. The ability to influence carbon decreases as the project progresses through the life cycle. For a new 25km highway project in the United Kingdom the CO2 emissions from vehicles using the road during the ‘use phase’ made up 94% of the total project CO2 over a 60 year period. This paper considers the effect of highway alignment, a decision taken early in a project, at the planning stage, to understand how it can positively influence the CO2 associated with the use phase. To understand the effect of the vertical alignment through the life cycle, the CO2 in both the construction and use phases have been calculated. A methodology to calculate the CO2 from the earthworks operations has been developed. The instantaneous emission model, PHEM, has been used to calculate the CO2 from the vehicles using a highway. The assessment of both a theoretical terrain and a current project has demonstrated the potential benefits from amending the alignment of a highway. Benefits across the life cycle are dependent on the fleet mix, vehicle flow, and the duration of the use phase.