PORTLAND — Bike, pedestrian and vehicular traffic will change in the coming weeks as construction on the new Route 1 bridge begins in earnest.

Traffic lanes have already been narrowed to 12 feet and shifted toward Interstate 295 to give crews more room to work.

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The new Portland-to-Falmouth bridge spanning the Presumpscot Rover will be on the ocean-side of the existing bridge, and heavy equipment such as cranes will be used.

For now, cyclists and pedestrians can continue to cross the bridge using the dedicated sidewalk in the work zone, according to Carol Morris, project spokeswoman.

At the end of next week, a new five-foot path will be opened closer to the travel lanes, Morris said. The sidewalk will be separated from traffic by a metal barrier, which is currently being placed.

The speed limit will also be lowered from 40 mph to 30 mph by the end of next week, Morris said.

Since the travel lanes will have no shoulder, Morris said only experienced cyclists should travel in the 12-foot traffic lanes, which carry about 15,600 vehicles a day.

“Bicyclists should either walk their bikes on the multi-use path or they should move with traffic on the roadway knowing there is no shoulder,” she said.

The new patterns will last for the duration of the $23.5 million project, expected to be completed by Dec. 31, 2014.