Construction of the £145M Hindhead tunnel on the A3 in Surrey could start in 2008 after the scheme was declared south east England's top priority last month.
The South East England Regional Transport Board (RTB) has committed money to the A3 scheme after concluding there was no other option for funding the project.
It has decided against using private finance after the Department for Transport ruled it would have to account for the whole cost of the scheme as soon as it was completed. Transport secretary Alistair Darling established the RTB concept in 2004 to give regions more say in transport decisions.
In the south east, the RTB has an annual budget of £141M in 2007/08, rising to £150M in 2010/11.
As a result of the RTB's commitment to Hindhead, several schemes will be deferred by a year. These include £64M of improvements to the A253 and A256 in east Kent, a £64M dualling of the A21 between Tonbridge and Pembury and a £40M widening of the A23 between Handcross and Warninglid. Plans for a £12M rapid transit system in Brighton will be delayed by three years.
Darling will rule on the plans in the spring.