Suffolk County Route 39

Suffolk County Route 39 is a county-maintained arterial in Long Island serving central Suffolk County between western Smithtown and eastern Brookhaven. The route connects residential communities, commercial corridors, and links to regional highways such as New York State Route 25, New York State Route 347, and the Long Island Expressway. It functions as a local connector for commuters traveling toward Huntington, Stony Brook University, and the Port Jefferson Harbor area.

Route description

From its western terminus near Nissequogue River State Park, the alignment proceeds east through neighborhoods adjoining Sunken Meadow State Parkway and Nicolls Road. The corridor traces suburban fabric passing near Smithtown High School, St. James, and commercial centers anchored by Smith Haven Mall. Eastbound lanes traverse wetlands adjacent to Lake Ronkonkoma and cross tributaries of the Peconic River, with grade separations and traffic signals providing access to NY 25A and Commack Road. Approaching Stony Brook, the road skirts institutional parcels associated with Stony Brook University Hospital and connects to service roads feeding the Long Island Rail Road at Stony Brook station. Continuing southeast, the roadway intersects county arterials that provide routes to Patchogue and Blue Point before terminating near feeder roads for Montauk Highway and coastal communities of Shoreham.

History

The alignment has origins in 19th-century plank roads and colonial-era trackways that linked hamlets such as St. James and Setauket to maritime piers at Port Jefferson Harbor and Smithtown Bay. During the early 20th century, the corridor was upgraded under county initiatives tied to the expansion of Suffolk County infrastructure and the motor age, paralleling improvements to Montauk Highway and the construction of the Long Island Motor Parkway. Mid-century suburbanization associated with Levittown-era growth and expansions of Suffolk County Community College prompted capacity upgrades, signalization, and intersection realignments. Later projects coordinated with the New York State Department of Transportation and county planners adjusted the route near Nicolls Road to accommodate the opening of Commack Plaza and commuter traffic bound for Huntington Station.

Major intersections

- Western terminus — junction with local roads near Smithtown and access to Sunken Meadow State Parkway. - Intersection with New York State Route 25 providing east–west access toward Manorville and Queens. - Interchange with Long Island Expressway (Interstate 495) facilitating regional travel toward Riverhead and New York City. - Crossing at New York State Route 347 connecting to Commack and Central Islip. - Junction with Nicolls Road serving Stony Brook University and SUNY Stony Brook research facilities. - Eastern terminus — connections to feeder roads for Montauk Highway and access toward Shoreham and Wading River.

Former alignments and changes

Portions of the corridor once followed earlier alignments of county lanes that served agricultural estates owned by families tied to Smithtown Bay ferry operations. Realignments in the 1950s and 1960s removed sharp curves and straightened segments in coordination with suburban subdivision plats associated with developers influenced by practices seen in Levitt & Sons projects. In the 1970s, state and county corridor studies recommended bypass segments near Stony Brook to reduce congestion adjacent to Stony Brook Village. More recent widenings and shoulder reconstructions reflect standards promulgated by the American Association of State Highway and Transportation Officials and local implementation consistent with Metropolitan Transportation Authority commuter patterns. Several short spur connections and former at-grade intersections were closed or converted to signalized junctions during safety-driven projects sponsored by Suffolk County Department of Public Works.

Traffic and road characteristics

Traffic volumes vary seasonally, with peak flows driven by commuter patterns toward New York City transit nodes and recreational trips to parks such as Sunken Meadow State Park and beaches at Smithtown Bay. Typical cross-sections include two to four lanes with turning bays, bike lanes in selected segments, and sidewalks near commercial districts like Smith Haven Mall and main streets in St. James. Pavement maintenance cycles are coordinated with county resurfacing programs and federal funding mechanisms associated with U.S. Department of Transportation grant cycles. Enforcement and safety improvements — including signal retiming, pedestrian refuge islands, and high-visibility crosswalks — were implemented following collision studies involving local agencies and stakeholders from institutions such as Stony Brook University Hospital and regional planning entities like the Suffolk County Planning Commission.

Category:Roads in Suffolk County, New York