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
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
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.