The Glasgow Subway is expected to remain shut for an extra two weeks because of work delays, Strathclyde Partnership for Transport (SPT) announced today.
That would see the underground railway not re-opening until mid-August, with the shutdown extended to six weeks.
SPT said contractor Colas Rail would not finish work on time “due to a number of issues”.
They include the removal of old concrete taking longer than expected, but SPT denied claims it had been replaced with the wrong type of concrete.
A spokeswoman said flooding of tracks which lead down into the Subway from the Govan train depot caused by heavy rain had also hampered progress.
The circular system, which is used by more than 1 million passengers a month, has been closed since 2 July.
Upgrading includes to a junction connecting the lines to the Govan depot.
Other work includes to Cessnock Station, and tunnel repairs between Hillhead and Buchanan Street Stations.
The 120-year-old Subway last underwent such a major overhaul when it was closed for three years until 1980.
The latest work was arranged for the quietist time of the year, during the school holidays, with buses replacing trains.
Assistant chief executive (operations) Eric Stewart said: “This is the most significant engineering aspect of the whole modernisation programme, which is being built to last for another 40 years.
“This is a regrettable position and we are working with the contractor to pull back some of this lost time, as we endeavour to minimise any further disruption to our passengers.
“We apologise to all our passengers for this inconvenience.”