The bridge has been damaged in the past from heavy vehicles travelling along the Princes Motorway and scraping the concrete under the bridge.

Work started on Sunday to install a $450,000 height detection system to stop heavy vehicles with insufficient clearance from using the bridge.

The system will use a laser to measure the heights of passing vehicles as they travel southbound down the hill.

Once an approaching vehicle has been detected as being higher than the 4.6-metre clearance at University Avenue an electronic message sign conveys that information to the driver.

There will also be work done on the southbound side of the motorway to construct a pullout bay and modifications to the University Avenue roundabout.

Vehicles identified as overheight will then be able to travel into the new bay before being detoured via the modified roundabout in University Avenue.

Also, work is under way to improve drainage under the Princes Motorway by repairing a large underground pipe north of University Avenue.

A section of the southbound acceleration lane from Old Mt Ousley Rd and the deceleration lane to University Ave will be closed during work, with completion planned before university returns to ensure traffic queues are minimal.

The $350,000 project aims to improve motorists' safety south of the Old Mount Ousley Road intersection by increasing the capacity of the drain to limit water flow across the road.

Night work will take place until Thursday from 7pm to 6am, withday work on weekdays between 7am and 6pm until February 20.

Reduced speed limits will be in place.