BRIDGING COLD WAR GAPS
Span’s design should halt ice bombs
Specific design requirements mean that if a cable-stay bridge replaces the George Massey Tunnel, it won’t have the same issues with “ice bombs” as the Port Mann and Alex Fraser bridges, according to the Ministry of Transportation and Infrastructure.
“The key is making sure that any design figures snow and ice management into it and builds on the lessons we’ve learned,” said Norm Parkes, B.C.’s executive director for highway operations.
The Alex Fraser was closed again Monday for “safety reasons,” owing to the buildup of ice on the bridge’s cables.
Construction on the tunnel replacement is expected to begin next year. The 10-lane, three-kilometre bridge meant to replace the aging tunnel, which takes traffic under the Fraser River between Delta and Richmond, is supposed to be completed by 2022.
Though it hasn’t been finalized, it’s expected that the bridge will be a cable-stay design, like the Alex Fraser, Port Mann, Pitt River and Golden Ears bridges.
According to a statement from the ministry, that kind of bridge is “the most appropriate” choice based on the distance across the river, the prevailing seismic and geotechnical conditions, and the fact that the province wants a clear-span bridge with no piers in the river to minimize the impacts on the environment and marine users.
This is in spite of the problems on the Port Mann and Alex Fraser bridges, with ice and snow falling from and blowing off the cables during winter storms.
Weeks after the Port Mann Bridge opened in 2012, it had to close because motorists were injured and vehicles damaged by ice bombs falling from the cables that support the bridge. Part of the problem is that cables pass over the roadway.
Cable collars were installed on the bridge in the fall of 2013. They’re manually released to slide down the cables and remove snow before it can build up, with an eye to preventing a repeat of 2012, though last Monday’s snowfall caused problems for drivers again. About 50 people have called the Insurance Corp. of B.C. to make Port Mann Bridge-related claims since the snow first hit a week ago. The bridge, however, has remained open with periodic HOV-lane closures to deploy the cable collars.
The Alex Fraser Bridge is less prone to issues with falling ice because its cables are on the outsides of the travel lanes. However, when the wind is high it can blow ice off the cables onto the road. This has happened before, in 2005, 2008 and 2012. The Alex Fraser was closed Saturday for more than six hours to protect motorists from falling ice. The bridge was closed again Monday for “safety reasons,” said a government news release. The right lanes were closed in both directions just after noon, and the entire bridge was closed at 1:30 p.m.
“This full bridge closure is necessary to protect the travelling public, due to snow buildup on the cables and warming temperatures,” said the release.
“There is an increased likelihood that snow or ice may shed from the cables into all of the travelled lanes. Therefore, as a precaution, the ministry has closed the bridge to traffic.”
Motorists were urged to use alternative routes, but the closure caused a messy and slow rush hour. Cars inched their way through the southbound Massey tunnel and were forced to wait in heavy traffic at the Pattullo Bridge while a broken-down truck was towed away.
“A whole day ruined and wasted all due to traffic,” said Twitter user @mikeschmeee using #alexfraserbridge. He later tweeted: “The rage is strong within me. I now understand why Vancouverites riot when things don’t go their way.”
Parkes told Postmedia on the weekend that he doesn’t expect the Alex Fraser will need cable collars similar to those on the Port Mann.
About 95 claims have been lodged with ICBC in the past week because of ice falling off the Alex Fraser.
There have been no issues with the Golden Ears and Pitt River bridges because of their designs — the cables don’t pass over driving lanes — and their locations are further inland.
According to the ministry, if a proposal for the new tunnel-replacement bridge involves cables, they’re not permitted to cross over traffic. The specifications also require that the contractor be responsible to ensure that snow and ice don’t fall onto the roadway from any elevated portion of the bridge above the deck and as a minimum, require the builder to install cable collars similar to the Port Mann or “an improved alternative.”
When asked what other kind of mitigation could be used, Parkes said it remains to be seen what the emerging technology will be at the time. “There hasn’t been lots ... We’re the only ones that have been able to keep a cable bridge open in a storm,” Parkes said, referring to the Port Mann and its cable collars.