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Speed limits on Main South Road

Speed limits will vary as the project is nearing completion.

Traffic can travel on a new road surface but still have a project area under construction.

When a new road opens, speed limits are reduced for a period of time.

The main reason for these short-term changes is safety.

Reduced speed limits are put in place to allow any final work activities to be completed and to ensure the road surface is adequately prepared for higher traffic speeds.

Even after a road has opened to traffic, workers may still need to finish activities such as landscaping, kerbing, line-marking or pouring final asphalt. Reduced speed limits help to alert road users that they are entering a construction zone.

‘Wearing in’ a new road

A bitumen road is made up of layers; a foundation layer that is placed on the ground, followed by base layers, then a waterproofing prime coat layer, and a top layer of asphalt—or wearing course.

Once the wearing course has been laid, a period of lower speed limits is required to ‘wear in’ the new surface.

When roads open, the speed limit often starts at 60km/h, which allows the excess bitumen to safely wear off.

Initial reduced speeds allow the road surface to develop the appropriate traction for safe driving at higher speeds. The road must be tested and reach certain levels of skid resistance before the speed limit can be raised.

Testing the new surface

According to guidelines set by the Department for Infrastructure and Transport, lowered travelling speeds and appropriate signage must remain until the road reaches a certain level of friction and skid resistance—measured in grip units.

This is tested by a special friction tester which is towed at prescribed speeds while its grip and pull on the road is measured.

The road needs to achieve 0.35 grip units, which is the measure deemed safe for moving to a higher speed limit.

Once the road passes the appropriate skid testing, this is reported to the Department for Infrastructure and Transport who determine when the speed limit will be reset.