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Orientation: Interstate 81 runs from bottom right to top left, crossing the Saint Lawrence River at center on the south span of the Thousand Islands Bridge system. On the New York mainland, at bottom right, is NY 12. Westminster Park Road (Jefferson CR 100) runs from left to top along the south side of Wellesley Island. From it, alongside I-81, branches Island Road (CR 191) toward top left.
Exit numbers: Exit 50 from I-81 is for NY 12 to Alexandria Bay and Clayton. Exit 51 is for Island Road.
The interchange: The south span of the Thousand Islands Bridge System is a suspension bridge (see photo) having a main span of 800 feet and an overall length of 4500 feet. It is undivided, and only two lanes wide, being one of a handful of places on the Interstate system with these characteristics. Because of its narrowness, there is a minium spacing requirement between trucks on the bridge, indicated by special signals along the sides. The bridge system is maintained by the Thousand Islands Bridge Authority, which also maintains the New York State welcome center loacted at the south end of the bridge. The authority also owns Boldt Castle, a popular tourist attraction and historical site in Alexandria Bay (see photo).
The interchanges on either end of the bridge are both common forms. South of the bridge is a full cloverleaf interchange with NY 12, which has a short divided section through here. Notice, in particular, the sharp turn at the end of the ramp from NY 12 southbound to I-81 northbound. Just north of this, on the northbound side, is the toll plaza for the bridge, and on the southbound side is the welcome center, which is also accessible from the Collins Landing road. The interchange north of the bridge, on Wellesley Island, is a type of folded diamond interchange with CR 100 and CR 191 (similar to Exit 1 on I-481).
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Orientation: I-81 runs from bottom to top. Island Road (CR 191) enters at bottom and makes a left turn to end at I-81.
Exit numbers: From I-81, Exit 52 is for Island Road, DeWolf Point.
The interchange: Exit 52, the northernmost interchange on I-81, is a diamond interchange with the north end of CR 191, just south of the United States Customs plaza. The southbound exit ramp diverges in advance of the customs plaza and leads to the truck inspection booths. Passenger cars reach Exit 52 by making a sharp right turn just south of the customs plaza, while commercial vehicles must travel through the diamond interchange to reach I-81 south. On the northbound side is the World Duty-Free shop, just before the international bridge (another duty-free shop is similarly situated on the southbound side). The actual boundary lies in the narrow channel, called International Rift, between Wellesley Island (bottom) and Hill Island (top). This is bridged by a twin span of merely 90 feet, north of which the Candian customs plaza is visible.Canadian Crossing (right)
In Ontario, Canada, the road becomes King's Highway 137. The Canadian Crossing of the Thousand Islands Bridge System connects Hill Island to the mainland. It crosses over several smaller islands and consists of three spans, of which the largest is a suspension bridge of 750 feet. On the mainland, there is a five-ramp partial cloverleaf with the Thousand Islands Parkway. Grading is visible which shows the interchange to have once been a six-ramp partial cloverleaf, since reconfigured to reduce merging traffic at the southbound toll plaza.