The M25 Cobham site, located to the south of the M25 between junctions 9 and 10, received planning permission for a Motorway Service Area (MSA) from the Secretary of State following a lengthy public inquiry in 2002 and 2003. While the Highways Agency's policy stated that MSAs should be provided at no more than thirty miles apart, or less than this when it can be shown there is a needs case and a higher than normal incidence of accidents attributable to driver fatigue, the existing constraints on the M25 made constructing new access slip roads technically challenging.
BWB became involved in this project in 2006 to assist the developer on technical matters such as buildability, programming, procurement and costings. Although in receipt of planning permission, due to a change in design criteria, the geometric design of the MSA access works had to be reviewed.
BWB was also responsible for providing advice on the on-site proposals, the remit being to develop a layout which was geometrically acceptable, safe for all users whilst still achieving the commercial aspirations of the MSA operator.
A key challenge for BWB was to prepare an access design which incorporated north and south facing slips together with a linked under-bridge beneath the M25, which was acceptable to the Highways Agency while being considerate of all the many site constraints. This included preparing detailed applications for departures from standard to support the horizontal and vertical alignment layouts and advising on potential construction costs.