The Sagtikos State Parkway (also known as the Sagtikos or Sagtikos Parkway; known colloquially as "the Sag") is a north–south limited-access parkway in Suffolk County on Long Island, New York, in the United States. It begins at an interchange with the Southern and Heckscher state parkways in the hamlet of West Islip and goes north to a large cloverleaf interchange with the Northern State Parkway in the town of Smithtown, where the Sagtikos ends and the road becomes the Sunken Meadow State Parkway. The parkway comprises the southern half of New York State Route 908K (NY 908K), an unsigned reference route, with the Sunken Meadow State Parkway forming the northern portion. Commercial vehicles are prohibited from using the Sagtikos State Parkway, a restriction that applies to most parkways in the state. The parkway was proposed to help bridge a gap in the eastern part of the Long Island Parkway system. Construction began in 1949 with the opening of an interchange between Bay Shore Road and the Southern State Parkway. Work on the parkway itself began the following year, with plans calling for connections to three spurs: the Captree State Parkway (now Robert Moses Causeway), the Sunken Meadow Spur (Sunken Meadow State Parkway), and the Heckscher Spur (Heckscher State Parkway). The parkway was completed in 1952, closing the highway loop on Long Island. In 2001, a study by the New York State Department of Transportation (NYSDOT) called for the Sagtikos State Parkway to be widened to include new bus and carpool lanes from end to end. Route description The Sagtikos State Parkway begins at an interchange with the Southern and Heckscher state parkways in the hamlet of West Islip, just north of the Robert Moses Causeway's junction with the Southern State Parkway. Heading southbound, this junction is signed as exit S4. The parkway proceeds northward through the town of Islip as a four-lane divided highway, passing through residential parts of the adjacent hamlet of Brentwood to reach exit S3, a partial cloverleaf interchange with Pine Aire Drive. Just north of the junction, the highway passes over the Main Line of the Long Island Rail Road. Continuing northward through Islip, the Sagtikos Parkway leaves Brentwood ahead of exit S2, a connection to County Route 13 (CR 13, named Crooked Hill Road). The southbound exit serves CR 13 by way of access roads through the Pilgrim Psychiatric Center while the northbound direction uses