It’s hard to imagine traffic between Fenway Park and Longwood Medical Area getting much more fraught with traffic snarls: With Red Sox games, hospital vehicles, and joggers dashing across the intersections that cut through the Emerald Necklace, a drive through the area can get pretty confusing.

And it just got more so.

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Starting this weekend, a new traffic configuration is in place at the intersection of Boylston Street and Brookline Avenue as it converges onto the Riverway. The block of Brookline Avenue that straddles the Riverway, previously a two-way street, has been shut down to one way.

Only traffic running northeast from the Longwood Medical Area into the Fenway can drive straight through on Brookline Avenue; traffic flowing in the reverse direction must take a detour around the roundabout, first turning right onto Park Drive, and making the wide U-turn to get onto Riverway, where motorists are then able to turn right onto Brookline Avenue.

The detour will be in place for one year, said Mike Keegan of the US Army Corps of Engineers, the agency responsible for the construction work plaguing the intersection. The purpose of the construction project is to alleviate flooding from the Muddy River into the Fenway, a problem that has come up again and again in recent years.

The diversion of Brookline Avenue will allow construction staff to install a culvert underneath the road.