This video is a good reminder that intersection crashes don’t always end at the intersection.
A driver reacts to another vehicle or there is some collision. The vehicle leaves its intended path. And within an instant, roadside infrastructure becomes the next hazard in the chain of events.
It’s something we see regularly in our crash investigations, and something we think about as we design intersections.
Intersections are often cluttered with roadside hazards – light poles, utility poles, signal poles, sign supports, electrical cabinets, culvert ends and other road furniture. Yet these are exactly the locations where vehicles can be deflected from their intended path following a collision or evasive manoeuvre.
Most people just focus on the crash between the vehicles. But from a Safe System perspective, we also need to think about the crash that might happen next.
Research by the Centre for Automotive Safety Research (CASR) examined 78 detailed investigations of metropolitan intersection crashes and found that around one in five vehicles was involved in a secondary collision. Nine of those secondary impacts were more severe than the original vehicle-to-vehicle crash. The study also found that more than a quarter of vehicles travelled at least 15 metres after the initial impact, and around 10% travelled more than 27 metres. That’s a long way when there are poles, cabinets, signs and other unforgiving objects surrounding an intersection.
Where roadside infrastructure is required, making it frangible, breakaway, relocatable or shielded can significantly reduce crash severity. A frangible pole may not prevent the crash, but it can dramatically reduce the consequences when human error occurs.
Safe System design does more than just try to prevent the crash. It’s also about ensuring that when people make mistakes, those mistakes don’t kill or seriously injure.
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𝗧𝗵𝗲 𝗥𝗲𝘀𝗲𝗮𝗿𝗰𝗵: Doecke, S.D. & Woolley, J.E. (2012). Post Impact Trajectory of Vehicles at Metropolitan Intersections (CASR060), Centre for Automotive Safety Research, University of Adelaide.
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