2.29 In 2002, Kellogg, Brown and Root recommended that the Government should only widen the M25 in conjunction with measures to control demand. They estimated that if the Government widened the M25 without demand management, journey times would still be 5 per cent longer in 2011 than in 1997, and reliability 16 per cent worse. Traffic typically grows by 2 per cent a year on the M25 and experience from previous M25 widening schemes shows that additional capacity fills up quickly. For example, when the section between junctions 9 and 10 was widened, in the year of opening traffic grew to fill completely the additional capacity at peak-times.
2.30 The Agency expects the widening to increase average speeds in the opening year by 10 miles per hour, and reduce the accident rate per million vehicle miles by 1.5 per cent. Its analysis shows that, taking account of traffic growth and without demand management, the overall benefits to traffic throughput peaks in 2021, six years after the expected completion date of the construction. Thereafter, benefits fall as additional traffic fills up the road.
2.31 The Agency and the Department have not made significant progress since committing to explore demand management in 2003. The Agency favoured managing demand on the M25 through integration with the local road network.
2.32 The Agency initially considered it desirable that these demand management measures should be developed and agreed with local authorities by summer 2006. In December 2008, the Office of Government Commerce found that successful delivery of these measures appeared unachievable. It recommended changing the scope to a 'proof of concept' scheme. The Department is now working with local authorities in Surrey on a £40 million project to test a toolkit of measures to manage traffic in a coordinated way.
2.33 It is not yet clear, whether the more ambitious techniques to manage demand across the M25 and local road network will be feasible. The Agency is not expecting results from the demonstration project until May 2012, around the completion of the first sections of widening.
2.34 The Agency sees the demand management project as delivering additional benefits in reducing M25 congestion at additional costs. We note, however, that the early implementation of demand management is important to ensure that the long-term benefits of the widening project are maintained. There are risks to maintaining the long-term benefits of widening from the Agency's decision to widen without proving it could manage demand.