"The works are on schedule, and construction completion is expected in late 2008," said a spokesman for the Transport Infrastructure Development Corporation.

While the railway line was extended from Hurstville to Sutherland in 1885, it was not until 1939 that a one-track branch line to Cronulla was opened.

In 1985, the Gymea to Caringbah section was duplicated, with the remainder now under construction.

The corporation spokesman said that over the next few months, work would continue on the rail bridges at Old Princes Highway, Glencoe Street South and Merton Street, Sutherland; President Avenue, Kirrawee; Gannons Road, Woolooware and the Kingsway, Cronulla.

"Future works on rail bridges at Oak Road, Kirrawee, and Acacia Road (Princess Highway), Sutherland, are subject to the approval of a traffic management plan by Sutherland Shire Council," the spokesman said. "If approved, they are scheduled to start in early 2008."

Merton Street, Sutherland, would be closed between Morley Avenue and the Merton Street rail bridge for 24 hours to allow for night works at the rail bridge.

"This work is scheduled to occur between 6pm on Thursday, January 24, and 7am on Friday, January 25.

"These works are necessary to deliver and install new pre-made bridge structures using a large mobile crane.

"Traffic detours will be in place as there will be no road access during this activity."

The spokesman said the new RailCorp staff car park at Cronulla station was nearing completion.

Works would continue at Kirrawee and Woolooware stations, including construction of the footbridge, lift, concourse and station buildings.

The spokesman said the next track close-down was due to take place on the weekend of February 9-10.

Gannons Road between Denman Avenue and the Kingsway would be closed on that weekend for rail bridge works.