There is concern that National Highways is routinely underestimating the impact and cost of delays caused by the construction of new road schemes. It does this to skew the business case and secure approval.
National Highways when planning “enhancement” works on its network, as with any major project that spends public money, must draw up business cases and benefit cost ratios (BCR). Given that benefits claimed for roads schemes mainly come from the time saved by road users, the costs of the disruption to road users during construction work are also be taken into account, where they are going to be significant.
The Junction 10 on the M25 (M25/A3 junction at Wisley) started in 2022 and was due to end this year. However, in early 2025 the end date was revised to Spring 2026.
Last year Highways Magazine revealed that National Highways had rigged its estimates of the cost of construction delays when working out the scheme’s BCR. A 2017 appraisal produced a cost of £23m at 2010 prices, but when the company calculated the BCR in 2020, this cost had somehow dropped to just £11m – but without any explanation.
After the scheme was consented, a 2022 Traffic Management Plan (TMP) was produced giving a estimated cost of traffic delays caused by the scheme at £45m (at 2010 prices), based on a three-year construction time.
As Guildford residents know since construction started, disruption to the M25 and A3 has been very significant, probably far worse than predicted, with lengthy jams on both roads, while multiple closures over entire weekends have attracted national media attention after causing chaos and costing drivers time and fuel.
Highways Magazine published National Highways data, released under freedom of information laws, showing that vehicles were delayed by more than a million hours in the last six months of 2023 alone. Using the same methodology as National Highways uses to estimate journey time savings, the magazine put the total cost of the disruption caused by the scheme at around £100m (2010 prices) over a 3-year construction period.
The Royal Horticultural Society, which runs the nearby Wisley Gardens. In January 2025 it asked the government to compensate it for what it says will eventually be £11m in lost income[. Ministers refused the request, claiming that the impact of the scheme on RHS Garden Wisley was “considered from the project’s early stages in 2016” and that National Highways had “incorporated mitigation measures where possible”.
Large schemes are always difficult to estimate. But it is concerning that National Government organisations are so cavalier with estimates. Support in government schemes is low ranging from HS2 to proposals to expand Heathrow. Openness and honestly is required from large organisations.
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