The Robert Moses Causeway begins inside Robert Moses State Park, located on the western tip of Fire Island. From here, the highway heads north across the Fire Island Inlet on the Fire Island Inlet Bridge. On the north side of the inlet, the road changes from a two-lane undivided highway into a four-lane undivided highway as it enters Captree State Park and approaches a cloverleaf interchange with Ocean Parkway. The parkway becomes a five-lane divided highway with three northbound lanes and two southbound lanes in the vicinity of the junction.
The parkway then traverses the State Boat Channel Bridge by way of a 665-foot (203 m)-long bascule bridge modeled after the Mill Basin Drawbridge in Mill Basin, Brooklyn. The north foot of the bridge contains an unnumbered interchange to a private road on Captree Island, where the rest of the road is surrounded by protected land. On the section that crosses over the Great South Bay, via the Great South Bay Bridge, the New York City skyline can be faintly seen on a clear day. Originally a toll bridge, the remnants of the former toll plaza for the Great South Bay Bridge can be found on the north side in West Islip. At the cloverleaf interchange with NY 27A, the third northbound lane becomes the deceleration ramp, and from there the rest of the parkway is four lanes wide. Read more