August 13, 2010

MCKAY-COCKER CONSTRUCTION LTD.

The presence of the train tracks meant that shoring and formwork had to be done within very restricted space.

Raised roundabout nears completion in London, Ontario

RON STANG

correspondent

LONDON, Ont.

By the end of the year, London will have solved a longtime bottleneck and accident-prone intersection east of downtown with a raised roundabout, billed as the first of its kind in Canada.

London approved a plan to reconstruct the heavily-used junction — which sees Hale and Trafalgar roads join up immediately south of a three-track railway crossing — several years ago.

The intersection is awkward. Traffic moving east along Trafalgar dead ends at Hale and then jogs north and crosses the tracks for about 50 metres before turning east again on Trafalgar. Traffic on both Trafalgar and north-south Hale carry a minimum of 10,000 vehicles a day. The train tracks are among “the busiest” in the country with as many as 60 CN freight and VIA trains passing daily, Karl Grabowski, the city’s transportation design engineer, said.

What finally pushed the city to construct the separation were several deaths in a short time period. Slow moving freights from a neighbouring shunting yard had meant motorists skirted the lowered crossing gates.

But VIA trains were coming in at 80 kilometres per hour, so it created some issues, Grabowksi said. He said “it really hit home” when some cyclists and pedestrians died.

Originally, a raised signalized intersection was proposed. But that was costly so the project was put on hold.

But when the city’s consulting engineer, Delcan, suggested the separation could be done at considerable saving by designing a raised roundabout, the city was able to come up with money taking advantage of government stimulus.

The cost is $11 million.

Delcan principal Henry Houtari said what the roundabout “really did for us was allow us to reduce the length of the structure because of the different geometry.” The result was “we were able to save a couple of million bucks in the cost of the bridge.”

A roundabout also eliminates some operational costs such as signals and associated maintenance.

And roundabouts are safer. “I think the studies and the literature out there are pretty clear that roundabouts, with the reduced speeds, significantly reduce collisions,” Houtari said.

The roundabout is not very high, only four metres above ground, with the tracks about two metres lower than the original road surface, giving enough clearance for trains. There is only a six per cent ramp grade for a distance of almost 200 metres that motorists have to climb. Houtari said the grade is slight to allow drivers enough visibility.

“The key for us was to make sure that people approaching the roundabout could see what we call the yield line and the signage and pavement markings on the pavement surface,” he said.

“It has to be very clear to the driver that there’s a yield condition coming up. And then once they’re up there, they can see everything.”

At the ramp’s crest there is room for a couple of vehicles before entering the one-lane circle, which is wider than an average vehicle lane.

Phil Weber, project manager with Ourston Roundabout Engineering Canada of Richmond Hill, Ont. and a consultant on the project, said the roundabout, made of asphalt, will have a three- to four-inch raised concrete apron or “occasional strip” closer to the centre island. “Trucks can track across that if they need to but passenger car drivers wouldn’t normally use it,” he said.

Nate Fehrman, project manager for London-based general contractor McKay-Cocker Construction Ltd. said the key construction issue has been the cramped footprint while trains continue to move below.

“Safety precautions were a tremendous part of this project.”

The trains could not be interrupted. As a result, the site required complex formwork, with 40 truckloads of materials shipped in from across North America.

The formwork was so involved because of the rather large bridge deck and loading of concrete, all done while maintaining train clearances. The shoring is also more complex. Usually when a bridge is constructed crews can close opposite lanes with vehicle traffic shifted to the other side. But not here.

Fehrman said shoring not only had to be “strategically placed between train traffic,” the clearances to construct the formwork were “very limited” because the structure was to be as short as possible to minimize ramp build-up and reduce the number of adjacent expropriated properties.

More than 90,000 cubic metres of fill is also required for construction, much sourced from other area infrastructure projects.

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