Route 138 is a major highway in the Canadian province of Quebec, following the entire north shore of the Saint Lawrence River past Montreal to the temporary eastern terminus in Kegashka on the Gulf of Saint Lawrence. The western terminus is in Elgin, at the border with New York State south-west of Montreal. Part of this highway is known as the Chemin du Roy, or King's Highway, which is one of the oldest highways in Canada.

New York State Route 30 (NY 30) is a state highway in the central part of New York in the United States. It extends for 300.71 miles (483.95 km) from an interchange with NY 17 in the Southern Tier to the US–Canada border in the state's North Country, where it continues into Quebec as Route 138. On a regional level, the route serves to connect the Catskill Park to the Adirondack Park. In the latter, NY 30 is known as the Adirondack Trail. Aside from the state parks, the route serves the city of Amsterdam and several villages.