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    Starts & Stops

    Commonwealth Avenue bridge project returns in late July

    Traffic on the Massachusetts Turnpike.
    Craig F. Walker/Globe Staff
    Traffic on the Massachusetts Turnpike.

    Commuters coming into the city from the west should know the drill by now: Big traffic disruptions and detours are in order as the state completes the replacement of the Commonwealth Avenue bridge over the Massachusetts Turnpike.

    Later this month, officials will begin a series of road closures and traffic diversions to buy working room to replace the westbound side of the bridge; the eastbound side was replaced last summer.

    A long stretch of Comm. Ave. and the Boston University Bridge will close to cars. Shuttle buses will replace the Green Line. And the Massachusetts Turnpike will go on a major diet, reduced two lanes in each direction.

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    Here’s what you need to know about the summer’s biggest road project.

    1. 16 days of summer.

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    On the night of July 26, Comm. Ave. will close to cars from Kenmore Square to Packard’s Corner until Aug. 11. Cyclists and pedestrians will still be allowed through. The BU Bridge will close to cars the same night.

    The next morning, the Green Line will be replaced by shuttle buses between Babcock and Blandford streets.

    The Big One comes the night of July 27, when the Turnpike shifts to two lanes until Aug. 6.

    The heavy lifting is scheduled to run for just over two weeks, though some finishing work — such as sidewalk construction — will take another few weeks. Other more minor finishing work will run as late as next spring.

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    The $110 million bridge replacement is being done in two around-the-clock summer sprints, one last summer, one this year, rather than a more traditional project that would keep Comm. Ave. open but take as long as five years.

    2. Don’t get too comfortable.

    While there were definitely traffic backups last year, things went reasonably well. The Pike returned to full capacity weeks earlier than expected, traffic on the highway during rush hour was down as much as 30 percent, and ridership ticked up on the commuter rail — suggesting some drivers took a different route in. Meanwhile, state officials practically begged commuters to take a vacation during the project if they could.

    Now, state highway administrator Jonathan Gulliver is worried that the smooth sailing last year will lull drivers into a false sense of confidence this time around.

    “We’re a little concerned we’re going to be victims of our own success,” he said. “Last year went really well. It went really well because everybody took our advice and stayed away. That’s the only reason it went really well. . . . People absolutely need to find alternate routes.”

    3. What’s changed?

    There are a few differences from last year.

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    Pedestrians and cyclists crossing the BU Bridge from Cambridge will be detoured through a parking lot because of construction where the road meets Comm. Ave.

    The state is also ditching a massive crane it used last year that took weeks to assemble, and it will instead use smaller cranes. That should benefit drivers because last year officials had to shut down an entire lane on each side of the Mass. Pike lane just to set up the big crane a few weeks before the project started.

    Finally, last year’s work on Comm. Ave. also included Green Line track work. That doesn’t have to happen this year, so the closure of that road should be several days shorter.

    Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter at @adamtvaccaro.