Push to cut intersection speeds to 30km/h

RADICAL measures including cutting speed limits to 30km/h at intersections and using sensors on country roads to warn drivers of oncoming traffic are part of a national plan to make roads safer and lower the number of crashes and deaths.

An exhaustive report by Austroads, the nation's peak body for road transport and traffic agencies, studied impact speeds and angles, and the different crash types of side, frontal, rear and pedestrian, calculating severe injury probabilities for every type of intersection.

It found 30 per cent of crashes causing serious injury and death on Australian roads occur at intersections, but little had been done to design safer intersections.

Co-author of the report, Adelaide University road safety expert Jeremy Woolley, said it was imperative to cut speeds at intersections.

"We are trying to say if you want to guarantee safe outcomes (at intersections) you have to bring speeds down to 30km/h or 50km/h somehow,'' Mr Woolley said.

"Now that could be by speed limits, or road design."

The report recommends nine designs or "innovative solutions" to road engineers, including a number of safe roundabout designs, changing the approach angle of intersections, raised intersections and reduced speed limits.

Nine safe intersection from the Ausroads report.
Nine safe intersection from the Ausroads report.

Mr Woolley said the purpose of the two-and-a-half-year Austroads study was to provide a motorist, cyclist and pedestrian survival guide for road engineers across Australia when new intersections were built and old intersections revamped.

One of the most significant changes targets major country road intersections where traffic meets side roads at high speed. In future, 150m from major intersections lit speed signs, similar to those used near the Heysen Tunnels in the Adelaide Hills, will alert motorists to cut speed to 70km/h or 60km/h when an approaching car on the side road triggers sensors.

The report states a trial of this system had cut fatal and serious injury crashes by 79 per cent.

Mr Woolley said most cuts in speed would be achieved by traffic calming built into the designs, but speed limits would also be needed.

He said motorists should get used to more and safer roundabouts on the road as well as traffic calming at intersections.

A crash at the intersection of South and Torrens roads in West Corydon in 2009.
A crash at the intersection of South and Torrens roads in West Corydon in 2009.

"The change of thinking is that too often we have looked at the likelihood of a crash. We put up a stop sign and that reduces crashes a bit but nobody ever steps back and asks 'what if a crash does occur?' and 'what if it was at a certain speed?,'' he said.

"So now we are trying to get engineers to focus on the consequences. Part of that is that if you can't change the intersection to make it safe you have to manage the speeds to make the crash at a safe speed.

"For pedestrians that is 30km/h, so in a CBD for example you would operate the whole system to have 30km/h in intersections. In other areas you would be slowing to a maximum of 50km/h.''

Mr Woolley said city traffic would be slowed with raised intersections similar to an example used in the report at the corner of The Parade and Rundle St in Kent Town. Raising of the entire area by 10cm had slowed traffic without the need for a changed speed limit and had almost eliminated serious crashes, Mr Woolley said.

The platforms act like speed humps and can reduce speed to 20km/h.

Mr Woolley said these would also be used more often before roundabouts and there would be numerous other changes to roundabout design.

The raised section of road on Rundle Street in Kent Town, which has slowed traffic.
The raised section of road on Rundle Street in Kent Town, which has slowed traffic.


Ripple strips would also become more frequent on country roads before intersections and pedestrians would be redirected and stopped from crossing at more intersections.

The report found that by using designs which had the least impact on drivers, the community "in many cases" may "accept much lower speed limits to facilitate safe and efficient non-vehicular traffic (10-30km/h) in a vibrant urban environment''.

Mr Woolley said the aim of the design and speed limit changes was to cut crash speeds to below that which cased serious injuries and deaths.

He said the CBD intersection speed of 30km/h would be needed to save pedestrians in the suburbs, and country car speeds would be cut to 50km/h for side-impact intersections and 70-80km/h where a head-on crash was possible.

"That is 30km/h through the (city) intersection, so generally for pedestrians if you have collisions at that speed they are generally survivable,'' Mr Woolley said.

"That is the threshold for injury and we should only allow faster speeds at intersections if we can guarantee safety in other ways (by design)."

Austroads is run by Australian and New Zealand federal, state, territory and local governments.

Its report, titled Understanding and Improving Safe System Intersection Performance, has been agreed to by all and will now be the standard design document for all intersections.




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