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 Ontario Highway 137 (Highway 137) links it to Highway 401. In the US state of New York, I-81 extends 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.
South of Watertown, I-81 closely parallels US Route 11 (US 11), the main north–south highway in Central New York prior to the construction of I-81. At Watertown, US 11 turns northeastward to head across New York's North Country region while I-81 continues on a generally northward track to the Canadian border. From there, the road continues into the province of Ontario as Highway 137, a short route leading north to the nearby Highway 401.
The portion of I-81 in New York was originally developed as the Penn-Can Highway, one of four expressways proposed by the state in 1953. It was added to the Interstate Highway System and designated I-81 in 1957 and constructed in sections over the course of the next decade. The first segment was completed in the mid-1950s, running from Tully to the southern edge of Syracuse. The last piece opened in the late 1960s, linking Marathon to Whitney Point.
Route description
Southern Tier
I-81 crosses the New York–Pennsylvania border about southeast of the city of Binghamton. The freeway heads northwest from the state line, running through a valley surrounding the Susquehanna River in the town of Kirkwood. This stretch of I-81 closely parallels US 11, continuing a trend that originally began at I-81's southern terminus in eastern Tennessee. Both roads head across relatively undeveloped areas along the eastern riverbank to the outskirts of Binghamton, where I-81 merges with New York State Route 17 (NY 17; Future I-86) in an industrial area east of the city. I-81 and NY 17 overlap for , running along the northern edge of the Binghamton suburbs before entering the city itself. About north of downtown, the freeway connects to Brandywine Highway, a limited-access road carrying NY 7 through mostly residential areas on the north side of the city.
Just west of the Brandywine Highway junction, I-81 and NY 17 cross the Chenango River as they split at a directional T interchange comprising part of an S-curve in NY 17 known locally as Kamikaze Curve. While NY 17 heads west into the curve, I-81 proceeds northward along the west bank of the river, connecting to US 11 and passing by SUNY Broome Community College on its way into the suburban town of Chenango. Here, I-81 meets the western terminus of I-88 at a junction roughly north of Binghamton. Continuing on, the freeway intersects US 11 a second time before leaving the banks of the Susquehanna River and proceeding generally northwestward into increasingly rural areas of the Southern Tier. The route makes its way across a series of hills and valleys for to the village of Whitney Point, connecting to US 11 and two state routes of regional importance—NY 26 and NY 79—at two exits on the western edge of the community.
Continuing on, I-81 begins to follow the Tioughnioga River, a tributary of the Susquehanna, as it bypasses the nearby village of Lisle to the east. While US 11 runs across the base of a valley flanking the river, the freeway proceeds along the valley's eastern edge, overlooking the valley road on its way to the Broome–Cortland county line. Both routes cross the border at points just yards apart, beginning their transition from the Southern Tier region to Central New York. About from the county line, I-81 encounters the village of Marathon, situated inside the river valley at the junction of US 11 and NY 221. The freeway connects to the latter at an interchange just east of the village center before heading northwestward for across a series of moraines in another prolonged rural stretch. Along the way, I-81 passes between the Tuller Hill and Hoxie Gorge state forests, located near Messengerville on the western and eastern sides of the highway, respectively.