In addition to acting as designer's representative on the M25 Spur, consultant KBR led the highway and structures design of the Western Perimeter Corridor scheme and subsequently provided a design support role during its construction. The scheme involved the construction of a large grade separated roundabout, christened Welcome Roundabout, which links T5 to the M25 Spur Road.
The Welcome Roundabout arch takes the West Perimeter Road beneath the Welcome Roundabout. It is a proprietary precast reinforced concrete arch structure, supplied by Freyssinet. Approximately 130m long with a span of 17m, its tapered ends have allowed the structure to be integrated with the surrounding landscape.
The arch was erected over an eightweek period, significantly less than the more traditional solution for a grade separated junction.