Drivers in downtown New Bedford should be prepared for detours on Monday. The last block of Union Street will be closed to traffic for two weeks starting Monday Afternoon as the city pours concrete.

Cars trying to head north on Route 18 from downtown will be directed to Elm Street, which will reopen permanently as a four-way intersection. the changes are part of a series of alterations planned for the final phase of the Route 18 construction, which started in April 2011.