After inspections revealed severe damage to the infrastructure, Transport Quebec yesterday closed one lane of the two-lane southbound ramp that connects the Décarie (Highway 15) to the Turcot Interchange indefinitely.
The stretch of road is used by about 31,000 cars daily, many travelling from Décarie to the Champlain Bridge.
The one-kilometre section of the ramp reduced to one lane runs between the falaise St. Jacques in Notre Dame de Grâce and an area just south of the Lachine Canal.
At its highest point, the ramp is about 100 feet in the air.
Transport Quebec was urged to immediately close the lane yesterday afternoon by the engineering firms maintaining and monitoring the 43-year-old interchange, said Mario St. Pierre, a Transport Quebec spokesperson.
News of the emergency lane closing comes as Transport Minister Julie Boulet and Montreal Mayor Gérald Tremblay continue to tussle over the best way to replace the aging structure.
St. Pierre said inspections revealed "degradation in the concrete" in the horizontal structure under the asphalt. "You can't see it from the outside," he said. The problem does not extend across the entire length of the closed ramp. "Only a certain portion of it is faulty, about halfway" across the ramp, he said.
Engineers say the structure is safe for a single lane in the middle of the ramp. "The central lane is directly on top of the pillars, so this is the strongest portion of the structure," St. Pierre said.
No problems were discovered on the northbound ramp.
When will the second southbound lane reopen?
"We don't know how long repairs will last because we don't know what repairs we will have to do and how we will do them," St. Pierre said.
Transport Quebec expects the lane closing to cause major traffic bottlenecks.
The affected ramp is used by 1,900 cars hourly during morning rush hour and 2,500 cars in afternoon rush hour.
St. Pierre urged motorists to use public transit, carpool or change routes or commuting hours if possible. "We're advising people to stay away," he said. He said motorists who normally take Décarie to reach the Champlain Bridge should consider another link to the South Shore or another route to the Champlain.
Quebec is working on plans to tear down and rebuild the interchange and other parts of what's known as the Turcot Complex. The complex includes the Turcot - where Highways 15, 20 and 720 converge - plus the Montreal West, Angrignon and de la Vérendrye interchanges.
The entire complex is used by about 290,000 cars daily
After years of planning, Quebec and Montreal can't agree on the new Turcot.
Montreal put forward a new vision of the highway system last week that would cut car capacity and boost public transit. Quebec has said Montreal's plan comes too late and is too expensive, at $6 billion. Quebec's plan would cost $2.5 billion.
Quebec has given Montreal a detailed cost estimate of the city's proposal, Tremblay spokesperson Darren Becker said. He said the city was not ready to comment on the estimate yesterday as the figures were being examined.
Last week, Quebec said it wants construction to start on the new Turcot this fall and be completed by 2017.
The sudden Turcot lane closing will probably exacerbate Quebec motorists' wariness of the province's crumbling road infrastructure.
In 2006, the de la Concorde overpass collapsed in Laval, killing five people.
In the aftermath of that disaster, sections of several highways were closed because of deteriorating support structures, and aging overpass pillars were found to have insufficient steel reinforcement.
Montreal motorists have long been concerned about the safety of the Turcot, with its decaying concrete and exposed reinforcement steel.
The Turcot was part of a flurry of road building to prepare for Expo 67. The $25-million Turcot Interchange opened on April 25, 1967, two days before Montreal welcomed the world to Expo.