Interstate 81 (I-81) is a north–south Interstate Highway in the eastern part of the United States. Its southern terminus is at I-40 in Dandridge, Tennessee; its northern terminus is on Wellesley Island, New York at the Canadian border, where the Thousand Islands Bridge connects it to Highway 137 and ultimately to Highway 401, the main Ontario freeway connecting Detroit via Toronto to Montreal. The major metropolitan areas along the route of I-81 include the Tri-Cities of Tennessee; Roanoke in Virginia; Harrisburg and the Wyoming Valley in Pennsylvania; and Syracuse in New York.

The Thousand Islands International Bridge is an American-maintained international bridge system over the Saint Lawrence River connecting northern New York in the United States with southeastern Ontario in Canada. Constructed in 1937, with additions in 1959, the bridges span the Canada–US border in the middle of the Thousand Islands region. All bridges in the system carry two lanes of traffic, one in each direction, with pedestrian sidewalks.