U.S. Route 101
The nearly highway's northern terminus is in Tumwater, Washington: the route remains along the Olympic Peninsula's coastal perimeter west, north, and east; the northernmost point on the highway is in Port Angeles. The southern terminus of US 101 is in Los Angeles at the East Los Angeles Interchange, the world's busiest freeway interchange.
Maine State Route 101
SR 101 begins in the south at an intersection with US 1 in Kittery, just northeast of its intersection with SR 236, where US 1 Bypass meets its northern end. Near this intersection is the exits 2 and 3 interchanges from the Maine Turnpike. The route heads northwest, intersecting local roads as it passes east of the town of Eliot. SR 101 intersects with SR 236 and enters the southern tip of South Berwick. The highway continues a short distance northwest before crossing the Piscataqua River into Dover, New Hampshire. Upon crossing into New Hampshire, SR 101 ends and the road continues as unnumbered Gulf Road. Motorists following this road west will soon come across signage leading to New Hampshire Route 4 towards downtown Dover. No advance signage exists in the reverse direction, with Gulf Road simply transitioning to SR 101 upon crossing into Maine.