Repairs to the A6 at Desborough cost £1.7m, it has emerged.
The bypass re-opened on Sunday (September 3), almost eight months after it closed in January.
In March, Northamptonshire County Council said they had spent £500,000 - but a council spokesman says that cost is now £1.7m.
The council is now in discussions with the Government about funding for the works,
A council spokesman said: “An emergency closure was needed on the A6 for safety reasons and we would like to thank everyone for their understanding and co-operation during the closure which was necessary to carry out the repairs.
“The issues uncovered on the bypass section of the A6 in Northamptonshire are unusual and we are having discussions with central government about the overall cost and funding.”
The work on the A6 caused misery to many road users in the area.
Not only did commuters face diversions, but Desborough and Rothwell saw an increase in traffic as vehicles ignored official diversion signs.
Originally, the stretch over the River Ise was closed and was set to open by the end of February.
But further investigations found problems and voids near the railway bridge further along the bypass.
The closure was extended to April and then the end of the summer holidays - taking the total closure to an unprecedented 228 days.