Wollondilly MP Phil Costa announced the maintenance upgrade on Monday. It will be paid for by the state government.

He said the work on Appin Road, between Market Street and Brian Road, would ``lengthen the life of the road and provide safer conditions for all road users''.

``The road surface needs ongoing maintenance and this work will extend the life of the road and improve driving conditions,'' he said.

The work will be carried out at night to minimise disruptions to traffic, and is expected to be finished by Tuesday, March 30, weather permitting.

The night work will be carried out from 7pm to 5am, with temporary traffic lights and a reduced 40km/h speed limit in place throughout the work site.

Police from the crash investigation unit are appealing for witnesses to a serious crash at Appin on Saturday night. The crash happened when two vehicles travelling north on Appin Road collided about 10.50pm.

A 2-year-old boy, travelling in a Mitsubishi Magna, sustained serious head injuries and was flown to The Childrens Hospital, Westmead. A man, 27, driving the Magna was taken to Liverpool Hospital with head and chest injuries.

Anyone who witnessed the crash or who has information about the incident, is asked to contact the crash investigation unit or Crime Stoppers on 1800333000.