Unprotected Concrete Pillars – What Roadside Protection Is Warranted?

A recent fatal impact of an unprotected concrete pillar of the Highway 402 overpass at Glendon Road begs the question what kinds of roadside protections are warranted to prevent such tragedies.

There are standards that exist in Roadside Design Manuals that are generated in the U.S. and these standards are mimicked in similar manuals in Canada and Ontario. Similarly there are protocols for testing the kinds of roadside devices that need to be installed; the latest version of these protocols is called MASH, 2016 version, also a U.S. standard. The policies adhered to by Ontario’s Ministry of Transportation are generally unknown because of the secrecy with which they operate. The public’s right to be informed about the Ministry’s operations has been whittled down over the years making it more and more like a dark and secret society rather than a public department functioning in a democratic Canada.

Historically protection from impact generally considers how far the pillar is located laterally from the travel path of vehicles. At the Glendon Road site the pillar was likely located about 10 metres away from the road edge. Consideration is also given for the type road or highway such that roadways with a higher design speed need to have a wider band of protections on each side of the travel path.

Consideration is also given to the typical angle at which vehicles depart a roadway and this will vary depending on whether the road segment is straight or curved. It has generally been reported that about 20% of vehicles will depart at an angle not  greater than 17 degrees. The basis for that belief has not been identified. A study of Highway 401 collisions conducted in the 1980’s by the University of Western Ontario Multi-Disciplinary Accident Research Team was presented by Zygmunt M. Gorski at an inquest to median cross-over collisions in 1989. That study showed that average departure angles were 13 degrees with the smallest being 3 and the largest being 36 degrees.

Consideration is also given to how far vehicles are known to travel after they depart a road edge. Historically it has been believed that only about 20% of vehicles travel a distance greater than 135 metres. The UWO Accident Research Team study showed an average distance of only 58 metres, the shortest being 22 and the longest being 104 metres.

Finally, it has been understood that only about 20% of vehicles travel a lateral distance of more that 9 metres from the travelled edge of the road. The UWO Accident Research Team study showed an average lateral travel distance of 8 metres; the shortest being 2 and the longest being 36 metres.

When these facts are combined a recommended “clear zone” is developed for different roadways.

With respect to Highway 402, it is believed to have a design speed of 120 km/h. The Glendon Road collision location contains a shallow right curve with a radius that is greater than 1000 metres and therefore it is recommended that the required clear zone not be adjusted to accommodate the presence of the curve. Its traffic volume (AADT)  has risen from about 10000 in 1988 to over 22000 today. Thus it is well above the threshold to place the clear zone in the highest category. The result is that any obstructions within 10 metres of the roadway should have required protection from potential impact.

When the overpass pillar is at the threshold for protection there is a general consensus that engineering judgment should apply. This loose term is often included in various manuals of standards and guidelines. It simply means using one’s trained and experienced common sense. Applying that engineering judgment should have recognized that the traffic volume of Highway 402 had risen over the years and that the daily 22000 vehicles that passed through the Glendon Drive location was too large to allow the unprotected pillar to remain unprotected. The fact that no one raised the issue is because essentially no one outside of the select few who study roadway safety standards would be aware of what is needed and acceptable. An uninformed public cannot complain when it does not recognize that there is a need to complain. And a single death is only highlighted in the news media for a day or two before it becomes lost in the ever greater quantities of information about less relevant matters.