Part of Cross Street in Somerville will be closed to traffic until November as crews work to replace a bridge. Westbound traffic must detour onto Tufts Street, to Washington Street, and then to McGrath Highway north before rejoining Cross Street on the west side of the bridge. Eastbound traffic will be sent to McGrath Highway north, then right onto Pearl Street, rejoining Cross Street on the east side of the bridge. A temporary pedestrian bridge was installed earlier this month to keep the street open to foot traffic. The work is being done by the Massachusetts Department of Transportation as part of its rapid bridge replacement program.