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Main Roads Western Australia wanted to compare driver behaviour before and following the installation of 4 new compact roundabouts in Osborne Park as part of the Urban Road Safety Program. The purpose of the Urban Road Safety Program is to introduce low-cost road safety treatments that modify driver behaviour. Specifically, they wanted to look at differences in car movements, speeds, and braking behaviours before and after the installation. GHD was the consulting partner for this project and provided their technical services as part of delivery.
In this case, the treatments are intended to reduce driver speeds through the treated intersections, and potentially reduce speeds between the treatments. This is intended to reduce near-miss events with lower-cost and faster-to-implement treatment methods by painting the roundabouts instead of installing a raised platform.
Image: GHD
Using average speeds, vehicle turning movements, and average braking (g-forces) on the approach to intersections at these 4 locations, the client was able to confirm the effectiveness of the treatments and compare the before and after periods.
Average G-forces before and after the intervention. Image: GHD
There was a small decrease in braking between the before and after periods on the entries to the intersection that were subject to a stop or giveway control (blue boxes). It’s likely that drivers were not coming to a complete halt before navigating the roundabouts.
Overall, the intersections are operating more safely and efficiently with average speeds below 50km/h. The energy involved in any potential future crashes is lower and is far less likely to have a serious outcome or result in serious injury. The lower-cost painted roundabout was just as effective at reducing driver speeds as a raised roundabout.
Speed data for different turns and between intersections. Image: GHD
The compact painted roundabouts have been shown to manage vehicle speeds below safe systems thresholds.
The Connected vehicle data provided a better insight than otherwise obtained through strips or road loops, which couldn't be installed at the conflict points because it was in the middle of intersections. The data provided insights into driver behaviour as they travelled through the intersection rather than at the midblock, measuring data directly at the conflict point. The presence of the loops also often impacts driver behaviour and affects any data recorded.
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