The £161m budget to upgrade Oxford Station and replace the railway bridge is under review.
Network Rail said it “cannot confirm any changes to the overall cost of the scheme” until further investigations have been carried out.
The work has caused significant disruption in Oxford, closing the Botley Road under the rail bridge since April 2023.
The road was due to reopen in October, but the date has been pushed back indefinitely due to “highly complex” pipework.
A new date for the reopening of Botley Road has not yet been confirmed.
Network Rail said its review would look at “what has been achieved so far, what remains to be done, plus the timescales and budget required”.
It said it would also “consider options for rescheduling the replacement of Botley Road bridge”.
“Work is continuing on the ground at Botley Road and our focus remains on finding the best way forward to deliver the benefits of this major programme for Oxford,” a spokesman said.
“We are working with the Department for Transport and local authority partners as we undertake a full review of the programme and will provide an update on timescales for the next steps of the project.
“This is an incredibly complex project, involving multiple organisations, so although we know everyone wants clarity, we are taking the time to get it right.”
The delays to the project have had a knock on effect on Oxford’s traffic filter trial.
Oxfordshire County Council had planned to install six new filters across Oxford in November.
But it said it first needed Network Rail and the Department for Transport to confirm when the Botley Road work would would finish.
It said it was “deeply dissatisfied and frustrated” about the situation.