Enhancements to England’s motorways and major A roads will cost billions of pounds more than planned, a report has found.
This includes plans to build a tunnel underneath the Stonehenge World Heritage Site in Wiltshire and the proposed Lower Thames Crossing.
Public spending watchdog the National Audit Office (NAO) said delays and inflation mean government-owned company National Highways will not be able to deliver dozens of projects within budget.
The report warned it will cost an estimated £3.3 billion more than planned to complete projects due to take place in the second road investment strategy (RIS2) between April 2020 and March 2025.
It also stated that projects due to be in construction during the subsequent five years are likely to cost £6 billion above previous expectations, although that includes some of the schemes included in the £3.3 billion figure.
Building the three kilometre road tunnel underneath the Stonehenge heritage site, to reduce congestion, could now cost up to £2.4 billion.
That's millions more than the previously anticipated price tag of up to £1.7 billion.
Meanwhile, the cost of building the UK's longest road tunnel to ease congestion on the Dartford Crossing has risen by almost two billion pounds since 2020.
It takes the price of the proposed Lower Thames Crossing connecting Kent and Essex up to £9 billion.
Neither have received development consent.
Some 33 schemes are behind schedule by between one month and more than three years, with an average delay of 12 months.
“This will leave road users with an underperforming road network for longer,” the report warned.
Delays have been caused by factors such as the coronavirus pandemic and difficulties obtaining planning permission.
National Highways was given a total of £14.1 billion by the Department for Transport (DfT) for 69 enhancement schemes in RIS2.
It has completed less work and at a higher cost than anticipated, the NAO said.
Last year, the budget for enhancements was cut by £3.4 billion and the number of projects were reduced to 58 when it became clear National Highways could not implement the delivery plan as intended.
The NAO also found that National Highways has already allocated all of its £1.16 billion RIS2 contingency budget.
Gareth Davies, head of the NAO, said it was “unfortunate” that the road investment plan developed by the DfT and National Highways coincided with the coronavirus pandemic and rising inflation, but “more could have been done to manage risks”.
He went on: “Delays to projects have meant that less work has been delivered than planned and at a higher cost.
“DfT and National Highways must now fully address the rising cost of its revised portfolio of projects, undertaking a review of all road plans that it plans to move into the time period of its third road strategy (2025-2030).
“This review must consider if these projects remain feasible and provide optimal value for money.”
National Highways chief executive Nick Harris said, “external factors” have had a “significant impact on our ability to deliver this complex programme”.
He added: “Despite these challenges, we have successfully received consent to deliver several major infrastructure developments.
“We’re confident that we manage portfolio and project risks well, while recognising that there is always room for improvement as we mature our processes ready for RIS3.”
A DfT spokesman said RIS2 is “transforming our road network” and a “minority of projects” are being delivered later than originally proposed.
He added: “We have allocated £24 billion to ensure we have a road network that is safe, reliable, environmentally conscious and good value for the taxpayer.”
RAC head of roads policy Nicholas Lyes said drivers will be “very frustrated if vital improvement works are put on hold”.
He continued: “Any attempts to take an axe to the roads budget is short-sighted because slow-moving traffic and delays do nothing to help the economy grow.”
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