WINDSOR, Ont. — The fact there were two truck rollovers within the same number of weeks at a newer roundabout outside Windsor this spring could be indicative of any number of factors, say police and roundabout design experts.

Municipalities are increasingly building roundabouts within cities as a way to curb severe accidents and manage traffic more efficiently. But in this case the roundabout is outside the city and connects two major provincial highways – Hwy. 3 and Hwy. 401. And it’s circulating not just motorists but a high volume of trucks as Hwy. 3 links to the Ambassador Bridge, Canada’s busiest commercial border crossing.

Indeed, hundreds of trucks a day now use the roundabout, which opened last June. But much of this traffic, especially that coming from the border, will cease once the new Rt. Hon. Herb Gray Parkway – the 11-km extension of Hwy. 401 – opens, perhaps late this spring. The roundabout will then be used primarily by local traffic.

(While the Parkway is designed to connect to a new bridge to Detroit the bridge itself is still in the planning stage and not expected to open until 2020. Traffic will still have to exit the Parkway to use the Ambassador Bridge before that date).

In at least one of the two accidents OPP said it appeared the load, containing non-hazardous materials, shifted.

Parkway spokesman Garfield Dales said the roundabout, located in suburban Tecumseh, “has been designed to Ontario’s high standards” and includes a four-metre wide truck apron around the central island for vehicles requiring more turn radius. It also has two 5.5-metre wide lanes and a 65-metre wide diameter.

The posted speed limit is 30 km/h.

Dales said the roundabout was designed to handle all types of traffic including trucks, buses and other large vehicles. 

“A large semi-trailer is typically used as the design vehicle however,” he said. “At locations where oversized vehicles are anticipated, special considerations for the size and tolerances of these vehicles are provided in design and construction. If oversized trucks or farm vehicles are known to be travelling through the roundabout, then they are modelled to ensure that their turning paths can be safely accommodated.”

Dales said “a main design feature” of the roundabout is the truck apron, considered by engineering experts as among the optimal features in roundabout construction. This allows trucks a sort of extra left lane over which their inner wheels can track as they negotiate the turn.

Dales, director of MTO’s Windsor Border Initiatives Implementation Group, said there has been plenty of education about use of the roundabouts including public meetings and instructions on the hgparkway.ca Web site. There is also MTO’s How to Drive in a Roundabout brochure available across the province.

“MTO has also reached out to our partners like the Ontario Trucking Association (OTA) to help spread the word,” he said.

The OTA, in fact, has been proactive on the roundabouts front.

In 2010 the OTA published a 24-page discussion paper, produced by consultants HDR and iTRANS, called Accommodating Commercial Vehicles in Roundabouts.

“It creates some geometrics that recommend roundabout design that takes into consideration all vehicle spec’s, so whether its tandems, tris, long combination vehicles, straight trucks, whatever,” OTA’s vice-president of communications Marco Beghetto said. “This is sort of the one-stop-shop for roundabouts, this is the roundabout (design) that we think will accommodate all vehicle configurations.”

Beghetto said when OTA learns of a jurisdiction planning a roundabout it contacts that municipality. “And for the most part they’re grateful – they’re grateful to have it and they use it and it works with great success.”

The OTA has also been campaigning for electronic stability control systems to be built into new trucks. Federal transportation minister Lisa Raitt said in March her government endorses the technology and is committed “to align with US vehicle standards.”

The technology, which can cost between $600 and $1,000, senses shifts in weight equilibrium forcing the truck to correct itself.

“Many of our members already use it voluntarily,” Beghetto said. “But most people consider it cheap insurance.”

Raynald Marchand, general manager for programs at the Canada Safety Council, said roundabouts prevent serious accidents like T-bone intersection collisions. Sideswipes in roundabouts, should they occur, happen “at typically lower speed,” resulting in less severe injuries.

But, Marchand said, roundabouts “are still pretty new” across the Canadian road landscape.

“And there are some roundabouts that were built just too tight and some of them had to be modified or improved or enlarged for some of the trucks that are out there,” he said.

That means, in certain situations, a truck, instead of just staying in the left lane and using the apron will need to use both lanes, creating a potential hazard.

“In using both lanes other traffic may be trapped by the fact the truck and trailer are using both lanes and be substantially sideswiped as a result of it,” Marchand said. “It’s important for the truck driver to plan it and to check for blind spots and so on if he or she is going to use both lanes.”

Marchand said some roundabouts have had to be modified.

“I know that up in Val-d’Or, Que. the one at the entrance there was just built too tight for large trucks and had to be redone,” he said. “So there is sometimes some engineering that needs to be put in place to accommodate large trucks. I think they’re getting better at it.”

Marchand said motorists also have to be prudent. “They change lanes in the roundabout and they don’t know exactly where to go, where they should be.”

Sgt. Kerry Schmidt, spokesman for the OPP’s Highway Safety Division in the Greater Toronto Area, said he can’t think of any roundabouts on OPP-patrolled highways in his region. But, he said, speed may be a factor as it is in freeway ramps incidents. While there could be design or poor signage issues, as well as driver unfamiliarity, “really there’s no excuse for a truck to roll over on and on and off ramp,” Schmidt said.

Madison, Wisc.-based GHD Inc. is a leading roundabout design firm with experience in Canada.

“A well-designed roundabout will address load-shifting problems with larger vehicles,” principal Mark Lenters said. “Problems such as inadequate entry deflection leading to high entry speeds, long tangents leading into tight curves, sharp turns at exits, excessive cross slopes (gradients for water runoff), and adverse cross slopes have been the principal causes of load shifting.”

Lenters said “a combination” of these elements can create the “tipping point” for a rollover. “No one element on its own is generally causal, which implies that removing one of the mechanisms from a combination of several…may be sufficient to remedy the problem,” he said.

Lenters said education “plays an important role” in preventing truck rollovers.

“Driver adaptation is making progress in Ontario,” he said. “But it is slower than adequate to avert some avoidable accidents.”