Using Connected Vehicle data to understand spillback and improve back-of-queue protection on highway offramps.
This case study uses Compass Road Intelligence
Transurban - one of the world largest toll road operators - wanted to understand where unsafe road conditions and near-misses were happening on the M7. In particular, they wanted insight into g-force data to for risk profiling across different sections of the network.
On the Glendenning portion of the M7 near the Richmond Road off-ramp exit, Transurban’s engineers could see near-misses on the mainline, caused by traffic on the off-ramp.
Traffic had slowed on the offramp and caused a spillback onto the mainline. The spillback led to 72% of near-misses occurring in peak hours. Engineers hypothesised that the spillback onto the mainline was causing drivers to brake and swerve to avoid other drivers at the back of the queue.
A year later, these near-misses translated into actual crashes, with 89% of crashes happening in the peak. Most of these crashes were rear-end crashes, caused by drivers on the mainline crashing into the back-of-queue vehicles using the offramp. They also found that when the M7 motorway was congested in the shoulder period, the number of collisions increased.
By using Compass data, Transurban was able to campaign for traffic light phases to be changed at the intersection at the top of the offramp. By giving more time for drivers to exit the offramp, it would prevent spillage onto the mainline and increase safety for all drivers on the joining roads, even if motorists have to wait slightly longer at the intersection lights.
After reducing spillback onto the mainline, there was a significant reduction in near-misses at the location leading up to the offramp.
