 The majority of NY 18's routing south of the village of Lewiston was incorporated into the U.S. Highway System in the early 1930s after US 62 and US 219 were extended into New York and US 104 was assigned. NY 18 now began concurrent to US 219 at the state line and overlapped the route northward to the city of Salamanca. US 219 left NY 18 here, and the latter continued independently to the town of Dayton, where it intersected US 62. From there, US 62 followed NY 18 north to a junction with US 104 (Main Street) in Niagara Falls. US 62 ended here, and NY 18 became concurrent to US 104 upon turning onto Main Street. The overlap ended in the village of Lewiston, where US 104 turned east to follow Ridge Road instead.
