In considering the possible impacts from the provision of east-facing slip roads at Junction 5 of the M25, the Highways Agency modelled the potential changes to future traffic flows at Junction 5 of the M25, and on the surrounding road network using available data.
This assessment suggested that (with the east-facing slip roads in place) the traffic flows in 2015 on the A25 between the A21 and the A227 would increase eastbound by 6 per cent. and decrease westbound by 11 per cent. Traffic on the A25 between the A227 and Wrotham Heath would decrease by 8 per cent. eastbound and 15 per cent. westbound.
The Department for Transport set out its investment programme for Highways Agency national roads until 2014 in Britain's Transport Infrastructure: Motorways and Trunk Roads (January 2009).
Proposals for improvements to Junction 5 of the M25 were not prioritised for implementation and were remitted to our longer-term transport planning process to establish the spending priorities for transport across modes after 2014.
As part of that process, we have assessed the scale of future challenges facing our national transport networks. This concluded that the challenges faced at Junction 5 of the M25 are not of a sufficiently high strategic national priority to be considered further in the current study work to 2014.
The provisional estimated cost of construction of east facing slip roads at M25 junction 5, based on the design developed in 2004, is £77 million (at 2008 prices). However, in the absence of further detailed engineering assessments of the proposal, this cost estimate should be treated as indicative only.