Interchange of the Week
Monday, 19 February 2001
New York State Thruway - Exits 7, 7A and 8, Ardsley-Elmsford

Exit 7 (top left)

Orientation: The New York State Thruway (I-87) runs from bottom to top and NY 9A (Saw Mill River Road) runs diagonally from left to top right. Also visible at top left is the Saw Mill River Parkway, which at this point bridges the river for which it is named.

Exit numbers: Continuing from Week 16 along the New York State Thruway, the next interchange is Exit 7 for NY 9A to Dobbs Ferry and Ardsley.

The interchange: This is a half-diamond interchange providing connections to and from the south only, matching prevailing commute patterns.

Exit 7A (top right)
(click the image to enlarge)

Orientation: The New York State Thruway (I-87) runs bottom to top, while the Saw Mill River Parkway runs diagonally from bottom left to top right. NY 9A (Saw Mill River Road) enters alongside the Thruway at bottom, then curves away to the right. It continues generally parallel to the Saw Mill River and Taconic Parkways toward Elmsford and Briarcliff Manor. Mountain Road intersects the Saw Mill River Parkway at left center.

Exit numbers: Exit 7A (Saw Mill River Parkway) is signed from the northbound Thruway for Elmsford and Katonah, and from the southbound Thruway for Yonkers and New York.

From the Saw Mill River Parkway northbound, Exit 20 is for the New York State Thruway (I-87), north only. From the southbound parkway, Exit 20 is the at-grade junction with Mountain Road.

The interchange: In the New York metropolitan area, expressways (carrying mixed passenger and commercial traffic) often run parallel to parkways (carrying only passenger cars). Often, interchanges between the two will provide connections for same-direction travel only (e.g., northbound to northbound), since reverse-direction movements would be essentially redundant. The New York State Thruway and the Saw Mill River Parkway share a corridor through Yonkers and Ardsley, and where they part company, Thruway Exit 7A offers just such a connection.

The northbound Thruway exit ramp offers a high-speed connection to the Saw Mill River Parkway; the southbound exit ramp is somewhat tighter and requires a stop at its base, where Mountain Road also intersects. The most interesting ramp is that from the northbound Parkway to the Thruway. The area's topography, combined with parkway height restrictions, allows this ramp to cross under the Thruway while still rising high enough to cross over the parkway immediately beyond. Here it makes a sharp curve, then provides a long acceleration lane to resume high-speed travel.

At this interchange, besides all reverse-direction movements, there is one missing connection. That is, from the southbound Saw Mill River Parkway to the southbound Thruway. However, this connection can be made at Thruway Exit 8 by means of the Cross-Westchester Expressway.

A full-size image (215 KB) is also available.

Exit 8

Orientation: The New York State Thruway (I-87) runs from bottom to top left. The Cross-Westchester Expressway, also under the jurisdiction of the New York State Thruway Authority, enters at top right and ends at the Thruway interchange. Interstate 287 follows the Cross Westchester Expressway, and joins the Thruway mainline from this point west (left) to Suffern. NY 119 (Tarrytown Road) runs across the top right corner. The surface road crossing I-87 at bottom is Taxter Road, a Greenburgh town highway.

Exit numbers: Exit 8 on the New York State Thruway is for I-287 to White Plains and Rye. Exit 8A, from the southbound Thruway only, is for NY 119 and the Saw Mill River Parkway. This interchange is unnumbered on the Cross-Westchester Expressway, being its terminus.

The interchange: This interchange has been completely reconstructed in recent years and is shown here substantially complete. The new design provides multi-lane, high-speed through travel on either I-87 or I-287. It also features new collector-distributor roadways to segregate through traffic from that using the NY 119 and Saw Mill River Parkway interchange immediately to the east on I-287. (At top right, part of the westbound I-287 ramps to and from NY 119 are visible.) It introduces Exit 8A on the southbound Thruway, which follows the original ramp to I-287 eastbound but now only connects to the collector-distrubutor roadway. The new southbound Exit 8 is a high-speed left exit feeding the Cross-Westchester Expressway on the inside. Also visible are the remains of the old northbound Exit 8 ramp.

The interchange was originally built as a standard semi-directional T, which allows for only right-hand exits and entrances. The original ramps were set in deep rock cuts, most of which were removed with the reconstruction. An older interchange design, the directional T (see Week 8 for an example), would probably have required less excavation, since it involves left-hand exits and entrances for left-turn movements. But the New York State Thruway Authority maintains the highest standards for safety and efficiency in highway design, which has typically precluded the use of left-hand exits. This is no longer a concern with the configuration of Interstate 287 as a through highway in its own right, rather than as an exit from Interstate 87.

NOTE: Portions of the images on this page appear blurry and indistinct. This is a security measure undertaken by the NYS Office of Cyber Security & Critical Infrastructure Coordination to restrict access to imagery of certain "sensitive areas".

Includes information submitted by C. C. Slater.

Cross-Westchester Expressway,
Saw Mill River Parkway, and
New York State Thruway at Steve Anderson's
New York State Thruway Authority official site.

John Cairns writes:
"I think the observation that a directional T would have cost less is quite apt, considering the ledge that must have been excavated for the ramps at the "head" of the [original] T. The foresight shown in the '50s construction eliminates what would have been a nightmare-ish weave pattern where traffic from the Thruway southbound to the Cross-Westchester eastbound would have to all merge left…. Since I live in Massachusetts, I have often experienced the tremendous weave pattern that the directional T interchanges encourage (not fun)."

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