In 2019 VicRoads published an update to its supplement to the Austroads Guide to Road Design Part 6. The revised supplement no longer uses the concept of ‘clear zones’.
The concept of ‘clear zones’ was developed in the 1960s and 70s and has resulted in rigid hazards deemed ‘safe’ just outside a calculated distance from the edge line.
The Supplement now ascribes an ‘area of interest’ based on modern research and an understanding that risk reduces with lateral distance from the edge line, but is not eliminated at a fabricated distance. It recognises that some vehicles travel far further than the old ‘clear zone’, and that they are subject to rollover risk in cleared areas.
On high volume roads the preferred treatment is continuous flexible safety barrier at a 4 – 6m offset, which provides the greatest safety benefits to the community in most cases.
(always consider the context on a site specific basis including road user mix, grades, volume, surrounding land use, environmental and other factors).