Temporary access road optioneering and cost analysis

High Speed Two (HS2) Lots C2 and C3 covers a section approximately 80km long between the Chilterns and Warwickshire. To enable construction of these sections, it was identified that a temporary service road would be required along the length of the HS2 route.

An optioneering study was commissioned aiming to reduce construction costs of this element. This included the analysis of four different forms of road construction - two asphalt/concrete surfaced and two unsurfaced compacted granular material. In addition, an alternative fifth option was proposed inspired by treatments applied to granular roads in developing countries, which consists of a traditional temporary granular road with 20 mm of bitumen surface dressing.

Each type of construction was trialled and compared both for use on a subgrade of CBR 1% and a subgrade of CBR 2.5%. The findings of the paper show that the asphalt and concrete surfaced roads were most expensive to install but also most robust in both conditions. The unsurfaced granular road constructions were shown to be more expensive in the long run when accounting for maintenance costs compared to the newly proposed bitumen surfaced dressed option. The alternative bitumen surfaced dressed option also had several benefits over the unsurfaced granular constructions, such as a more skid resistant surface, lower dust pollution, higher possible longitudinal gradient, allowance for road markings and easier control of surface water run-off.

The study recommended the fifth option of surface dressed granular road. The balance of properties lends itself very well to a site access road that is temporary in nature but will extend for a long distance, be in place for a longer period of time and will undergo a significant number of axle passes. It is the lowest in cost out of all the proposed options but also retains many of the benefits of the more expensive heavy-duty access roads.