About the Robert Moses Causeway
The Robert Moses Causeway — officially the unsigned reference route NY 908M and known locally as simply “the Causeway” — is the truck-restricted Suffolk County parkway that carries traffic off the Long Island mainland, across the Great South Bay, and onto the western end of Fire Island. Roughly 5 miles long, it begins near West Islip at the Southern State Parkway and Sunrise Highway (NY 27) corridor, runs south to Captree State Park on the bay, and then climbs over the high State Boat Channel bridge to Robert Moses State Park on the Atlantic barrier beach. It is the only direct vehicular route to that stretch of Fire Island, and on a hot summer Saturday it is one of the busiest recreational roads on Long Island.
Construction history
The causeway is a product of the Robert Moses parkway-building era and was constructed by the Long Island State Park Commission, the agency Moses ran for decades. The crossing opened in stages beginning in 1954, finally giving motorists a fixed connection from the mainland to the new ocean-beach state park that would later be renamed Robert Moses State Park in 1964. The northern extension, linking the bay crossing up to the Southern State Parkway and the Sunrise Highway corridor, followed in the 1960s, knitting the causeway into the larger Sunken Meadow–Sagtikos–Robert Moses parkway spine. The iconic water tower at the southern terminus, standing over the Robert Moses State Park traffic circle, remains the corridor’s most recognizable landmark and a navigational reference for generations of Long Island beachgoers.
Route geometry and the bridges
From its northern end at the Southern State Parkway and Sunrise Highway near West Islip, the causeway heads south through the mainland edge of the Town of Islip and reaches the water. The first major structure carries the road across the Great South Bay toward Captree State Park, a bay-side fishing and boating hub on Captree Island. Past Captree, the road rises onto its signature span — the tall fixed-deck bridge over the State Boat Channel — before descending onto the barrier island and looping into the Robert Moses State Park traffic circle. Because so much of the route is open water and elevated deck, the causeway has very little of the roadside development found on inland parkways; it is, functionally, a bay crossing with parkway geometry.
Jurisdiction and patrol
New York State Police Troop L holds primary patrol and investigative jurisdiction over the Robert Moses Causeway, consistent with its authority over Long Island’s other state parkways. The road is maintained by NYSDOT Region 10 and remains owned by the NYS Office of Parks, Recreation & Historic Preservation. New York State Park Police and the Suffolk County Police Department (SCPD) assist at major incidents and at the park entrances during the busy season, but they are not the primary investigative agency on the corridor. NYS Police Troop L also enforces VTL §1180-c work-zone violations, where moving-violation fines are doubled.
Speed limits and the truck ban
The posted speed limit on the causeway is generally 50 mph, with lower limits at the bridge approaches, the Captree interchange, and the Robert Moses State Park entrance. As with nearly every New York State parkway, commercial vehicles and trucks are prohibited. The recreational-parkway design, the bridge structures, and the road’s beach-access purpose make it a passenger-vehicle-only route; commercial through traffic is directed to Sunrise Highway (NY 27) instead. During strong wind events the high State Boat Channel bridge may be restricted to passenger vehicles, closed to high-profile vehicles such as campers and trailers, or shut entirely.
Recent Editorial Coverage
Long Island Traffic data-desk and archive pieces that cover the Robert Moses Causeway and its corridor:
- Traffic Alert: Robert Moses Drawbridge Work Starts After Labor Day — bridge-maintenance delays on the causeway crossing
- Nassau vs. Suffolk: Comparing Crash Rates Across Long Island — profiles the Robert Moses Causeway beach-traffic season and the Sagtikos–Southern State merge it feeds
- Long Island’s Most Dangerous Roads: A Data-Driven Analysis — the ranking that places the Moses-era parkway network among the island’s highest-incident roads
- A Guide to Navigating Long Island Road Closures and Construction — notes the Robert Moses Causeway among the bridge crossings with multi-year reconstruction on the horizon
For the complete causeway accident archive, see /accidents/ and filter by road. The corpus includes a steady stream of NYS Police Troop L property-damage, personal-injury, and hit-and-run reports logged on the Robert Moses Causeway.