Residents of western Montreal are about to lose access to one of their quickest routes downtown.

On March 3, Transport Quebec will begin demolishing the onramp from St. Jacques St. to the 720 eastbound, and start closing lanes prior to demolishing the St. Jacques St. overpass.

Demolishing the onramp will force sections of Highway 15 and 720 to be closed for short periods of time, but Transport Quebec has not set dates for those closures.

The agency said as part of the onramp work most lanes on the bridge over the Decarie Expressway will be closed, but that it will keep at least one lane open in each direction until the bridge is taken down.

Until the bridge is removed, Transports Quebec is recommending drivers continue east on St. Jacques St. and access the Ville Marie Expressway at Cathedral St. in the downtown core.

Some may go another route, or use the next available highway entrance at Green Ave.

“This is what we suggest, of course people do their own planning, their own itinerary,” said Caroline Larose of Transport Quebec.

When the bridge comes down and until it is replaced, drivers who want to access the highway will either have to head 2.5 km west and enter the highway from Angrignon Blvd., or head 1.5 km north only to get on Decarie Expressway heading south.

Last year Transport Quebec agreed to delay the St. Jacques project, originally scheduled for August 2013, because Decarie Blvd. was still under construction.

That road in front of the new MUHC superhospital is still under construction with no end date in sight.

It is expected to take several years to replace the St. Jacques St. Bridge, which will end up about 1 metre lower, as part of the rebuilding of the Turcot Interchange.

In one spot of good news, Transport Quebec seems to have has listened to residents who have been demanding some way to access the 720 eastbound from Western Montreal.

The agency says plans have been modified and the new interchange will include an access ramp to the 720 east from Pullman St. in St-Henri, which runs along the bottom of the escarpment, parallel to St. Jacques St.

The new exit will be built in 2017.

Still, NDG-Cote-des-Neiges Mayor Russell Copeman predicts a big traffic mess.

“Everyone's going to be scrambling for alternate routes and there aren't that many east-west alternate routes,” he said. “We cannot have 21,000 cars a day merely shifting on to NDG Avenue or on Cote-Saint-Luc Rd.”

Copeman said Transport Quebec has yet to meet with him to discuss a plan.

“There is a cavalier attitude,” he said.

Transport Quebec said it hopes people will be patient and consider the future.

“They’ll see in the long term what they will gain from it,” said Larose.