The electronic sign only activates when it’s raining, and a vehicle is approaching. A sensor mounted on a pole detects rainfall every 20 seconds. At the same time, a radar detects approaching vehicles. Once the rainfall reaches a threshold of 1mm, the system becomes active and a flashing ‘slippery when wet / slow down’ sign lights up.
Developed as a cost-effective and flexible solution, the electronic sign provides an added layer of defence on slippery roads before resurfacing projects are undertaken.
WSP senior traffic and safety engineer Justine Wilton says the idea for the trial came from a growing frustration with the hazards posed by chip seals that become slippery due to the polishing of stones. Often, drivers are unable to see these polished stones, which can cause loss of traction, leading to crashes.
“It’s been observed that people tend to ignore static slippery when wet signs, leading to the idea for additional, attention-grabbing warning. This technology is about conveying a stronger message to drivers when the heavens open and it’s most critical for them to slow down.”
The trial, which began last December, initially targeted a curved site with patches of low skid resistance and a history of crashes into the median barrier.
Preliminary data shows a noticeable decrease in the speed of vehicles passing the electronic sign, and less crashes. The trial is now in its final stage, evaluating the combination of the electronic sign with a static sign to decide what results in the greatest speed reduction.
Both the sensor and the radar are powered by solar-charged batteries. The three-stage trial has so-far generated approximately 45,000 data points per stage, which are currently being analysed.
Justine says the beauty of the pole-mounted sensor system is that it can be easily relocated and avoids the need to cut sensors into road seal, which lets water into the pavement and involves costly traffic management.
As the trial enters its final weeks, she’s optimistic about the system's potential to enhance road safety on slippery road surfaces. The plan now is to adjust its settings to optimise responsiveness, such as determining the best timing and thresholds for activation during rainfall and draft a framework for how and when the system could be used.
