Interchange of the Week
Monday, 6 October 2003
Single Point Urban Interchange: NY 25 & CR 97, Centereach
A full-size image (263 KB) is also available.

Orientation: Suffolk County Route 97 (Nicolls Road) runs bottom to top, and NY 25 (Middle Country Road) runs left to right. This interchange lies between the communities of Selden (to the east) and Centereach (to the west) in the Town of Brookhaven.

The interchange: An inherent feature of the standard diamond interchange design (see Week 58) is that its ramps form two closely spaced intersections with the cross road. In a high-traffic location, these intersections are typically signalized, and left turns to and from them conflict with each other. Traffic congestion can often become severe as vehicles collect between the two signalized intersections. A relatively new interchange design that solves this problem is the Single Point Urban Interchange or SPUI.

Completed in 1999, the interchange featured here is the first SPUI constructed in New York State. Another is under construction on I-278 at NY 25A in Queens and a third has been proposed for I-81 at NY 3 in Watertown. In this design, there is a single intersection for all of the ramps, located directly above or (in this case) below the freeway. Note the channelized ramp ends, the disposition of turn lanes and the use of pavement markings through the intersection. This allows concurrent left turns, the most important characteristic in this design, from the surface road as well as from the ramps. The SPUI design greatly facilitates traffic movements on the surface road and reduces backups on the surface road and ramps.

Nicolls Road is itself notable for being a county-maintained road with controlled-access (freeway) sections, of which few examples exist. The longest example is the Bronx River Parkway in Westchester County, but almost all other roads of this type are State highways or New York City expressways and parkways.

Nicolls Road at Steve Anderson's
SPUI Interchange at Kurumi's Field Guide to Interchanges by Scott Oglesby.

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