The government has pledged a further £590m towards Britain’s biggest road-building project, the controversial and long-delayed Lower Thames Crossing.

In March, the transport secretary gave formal approval to the new road tunnel under the Thames joining Essex and Kent. The £9.2bn project will comprise more than 14 miles of roads including the 2.6-mile crossing near Thurrock, Essex.

The chancellor, Rachel Reeves, described the £590m as “critical funding” to take forward the crossing. The scheme would ensure “a smoother, less congested passage of vital goods from [mainland] Europe to our regions”, she said, adding: “This is a turning point for our national infrastructure.”

The transport secretary, Heidi Alexander, said the government was “finally getting on” with the crossing, adding that the “crucial project” had “been stuck in planning limbo for far too long”.

She said: “This project is essential for improving the resilience of a key freight route. It will speed up the movement of goods from south-east England to the Midlands and the north.”

National Highways, the arm’s length government body that runs England’s motorways and main roads, will be responsible for building the crossing. Construction could start as early as 2026, with the main works expected to take six to eight years.

The body’s latest financial statement said the long-delayed crossing would cost at least £9.2bn, of which £1.2bn has already been spent on design and planning work. The public-private option under consideration would cost £9.4bn, including £6.3bn of private investment.

It has disputed campaigners’ claims that tolls could triple if it is built using private finance.

The new funding for the crossing is part of a wider £1bn “structures fund” to be spent on repairing bridges, flyovers and tunnels across the country, as well as ensuring infrastructure is “more resilient to extreme weather events”.

The details come before a new 10-year infrastructure strategy, which is due to be announced by the government later this week.

Last week Reeves announced a £15bn package for trams, trains and buses outside London, which forms part of a £113bn investment in capital projects over the rest of parliament, including transport, homes and energy. Much of this money is expected to be directed towards areas outside the south-east of England.