In Brockton, Route 123 crosses Route 24 at exit 17. The route passes the Brockton VA Medical Center, Campanelli Stadium, Brockton High School and the Brockton Fairgrounds in quick succession. At the intersection of Belmont Street and Warren Avenue, the eastbound and westbound lanes split. Eastbound, Route 123 makes a quick turn on and then off of Main Street and crosses Route 28 (North Montello Street) and under the Old Colony railroad tracks before turning left and sharing a short, one-block long concurrency between Route 123 East and Route 27, before meeting the westbound lanes at the intersection of Commercial Street and Centre Street. The westbound lanes, meanwhile only intersect Routes 27 and 28, heading straight from Centre Street, across Main Street and along the short Legion Parkway before turning south onto Warren Avenue to meet up with the main route once more. Signage in the area is poor, however; many maps point to Route 123 begin concurrent along Route 28 rather than following Commercial Street on the other side of the tracks.