In South Portland, US 1 merges with I-295 at exit 4 and continues north through downtown Portland to Tukey's Bridge, now on I-295, before separating at exit 9.
The highway bridges the Sheepscot River in Wiscasset, the Damariscotta River in Damariscotta, the Medomak River in Waldoboro, and the Saint George River in Thomaston before reaching Rockland.