Motorists are being advised to expect delays and road closures on Castlereagh Road and Mulgoa Road throughout May.
Construction work is being carried out as part of the upgrade of Mulgoa Road at Penrith between Union Road and Museum Drive.
Work will be carried out between Wednesday, May 1 and Friday, May 31 from 7am to 6pm on weekdays and Saturdays from 8am to 1pm, weather permitting.
Some night work will also be carried out between 9pm and 6am.
To allow work on the railway bridge to be carried out safely, Castlereagh Road will be closed between Jane Street and Museum Drive from 10pm on Friday, May 24 to 6am Monday, May 27.
While the closure is in place, motorists will be detoured via the Great Western Highway, Coreen Avenue and The Northern Road.
Pedestrian and cyclist access will be maintained while the road closure is in place.
At other times, lane closures will be in place on the southbound lanes between Museum Drive and Jane Street and may affect travel times.
During lane closures, traffic control and a reduced speed limit of 40 km/h will be in place for the safety of workers and motorists in the vicinity of the works.