Interstate 81 (I-81) is a part of the Interstate Highway System that runs from I-40 at Dandridge, Tennessee, to the Thousand Islands Bridge at Wellesley Island in New York, beyond which the short 2.7-mile (4.3 km) Ontario Highway 137 (Highway 137) links it to Highway 401. In the US state of New York, I-81 extends 183.60 miles (295.48 km) from the Pennsylvania state line southeast of Binghamton to the Canadian border at Wellesley Island northwest of Alexandria Bay. The freeway runs north–south through Central New York, serving the cities of Binghamton, Syracuse, and Watertown. It passes through the Thousand Islands in its final miles and crosses two bridges, both part of the series of bridges known as the Thousand Islands Bridge.

King's Highway 137, commonly referred to as Highway 137, is a provincially maintained highway in the Canadian province of Ontario that connects the northern end of Interstate 81 in the U.S. state of New York with Highway 401 via the Canadian span of the Thousand Islands Bridge. While this road connected to the international bridge when it opened in August 1938, it was not designated as a King's Highway until 1965. Highway 137 passes through a portion of the Canadian Shield, a geographic feature which aided construction of the three Canadian spans of the Thousand Islands Bridge. These bridges, all of different designs, travel 538 m (1,765 ft) across the Saint Lawrence River. Highway 137 is 4.3 km (2.7 mi) in length and is located entirely within the United Counties of Leeds and Grenville.