Riverside Roundabout

Project Location: CR  94, CR 63, CR 104 and NYS 24 Riverhead
Client: Suffolk County Department of Public Works

Suffolk County Department of Public Works identified the five-legged traffic circle at CR 94, Center Drive, CR 63, Old East Moriches-Riverhead Road, CR 194, Quogue-Riverhead Road, and NYS 24, Flanders Road was operating beyond its intended capacity and had operational and safety deficiencies.  The project entails reconstruction of the traffic circle into a two lane modern roundabout with other traffic related improvements in order to accommodate bicyclists, pedestrians, and vehicle traffic safely and efficiently.

N+P prepared numerous conceptual alternatives to meet the goals of various design criteria including the elimination of one leg of the roundabout and avoiding major property acquisition. These conceptual alternatives included:

• Oval shaped roundabouts
• Side-by-side roundabouts
• Roundabouts with new adjacent intersections to eliminate a leg
• Two-lane “turbo” roundabouts

Traffic counts and intersection turning movements were collected and forecast to ETC and ETC+20. PTV Vissim and Rodel Software packages was used to perform capacity analysis and assisted in the selection and layout of the preferred alternative in close coordination with Suffolk County.

Several permits were required including US Army Corps of Engineers Nationwide Permits, a NYSDEC Atricle 24 Freshwater Wetland Permit, a NYSDEC Article 25 Tidal Wetland Permit, a NYSDEC Wild, Scenic, & Recreational Rivers Permit, and a NYSDOS Coastal Consistency Concurrence.

The design included, landscaping, LED streetlighting, signage design, pavement markings

There were a few significant design challenges with several design features:

• Work Zone Traffic Control – Construction of a modern two-lane roundabout while maintaining safe vehicular and pedestrian traffic flow through the intersection,
• Drainage design – With high groundwater, no vacant land for recharge, and DEC stormwater quality requirements, N+P provided two bio-swale areas, shallow leaching structures, and a stormwater treatment system that cleaned the stormwater runoff prior to discharging into the Peconic River.
• Access to adjacent properties – Large tanker trucks made deliveries to a gas station on the northeast corner of the roundabout. Permeable pavers provided access only for the tanker trucks to get access to the underground gas tanks while maintaining an aesthetic appearance.