Phase 1, which was awarded to Keolis in February 2019 and managed by Keolis Commuter Services in partnership with MBTA's Railroad Operations team, adds four miles of double track between Walpole and Norfolk Stations, to be commissioned in spring 2020.

Work will then begin on Phase 2, which will add three and a half miles of double track between Norfolk Station and Frank Street by December 2020. In parallel, preliminary design work will begin on Phase 3, focusing on the four-mile section of track between Walpole and Norwood Central Stations. Once Phase 3 is completed, a double-track line will extend along the entire section between South Station in Boston and Franklin Station.