Interchange of the Week
Monday, 13 November 2000
Monday, 13 November 2000
I-787, US 9 & US 20, Albany
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Orientation: The Hudson River separates the cities of Albany, left, and Rensselaer, right. I-787 comes in at bottom as an elevated structure over a branch of the Delaware and Hudson Railroad that serves the Port of Albany. I-787 descends through the interchange and continues out at top as a surface freeway with the rail line in its median. US 9 enters at bottom right (immediately adjacent to the Hudson River) and crosses the river on the Dunn Memorial Bridge (a photo of this dramatic approach is here). It turns north at the interchange, and leaves at top along the surface streets on either side of I-787: Quay Street on the east (northbound) and Water Street on the west (southbound). North of this photo, US 9 turns west at another interchange onto Clinton Avenue. US 20 overlaps US 9 over the Dunn Memorial Bridge, but proceeds straight through the interchange. It exits the freeway onto South Pearl Street and turns south, overlapping NY 32 for one block. It then turns west onto Madison Avenue and exits the photo to the west. The South Mall Expressway is the freeway running west from the Dunn Memorial Bridge. For part of its length, it carries US 20; the remaining segment is reference route 913V. It exits at top left, ending at the Empire State Plaza a short distance beyond.
NY 32 enters at bottom left on South Pearl Street, two blocks west of I-787. Between Madison Avenue and the South Mall Expressway ramps, it overlaps US 20. It exits at top, on North Pearl Street. NY 5 comes in at top, on State Street. It turns south onto Broadway opposite the State University administration building. NY 5 terminates at I-787, or more precisely, at its service roads, Water and Quay Streets. The terminus includes the northern of two underpasses connecting the service roads.
Exit numbers: From northbound I-787, Exit 3 is for US 9 south and US 20 east to Rensselaer (via the Dunn Memorial Bridge), and the Empire Plaza (via the South Mall Expressway). Exit 4 is for US 9 north (via Quay Street) and US 20 west (via the northern underpass, providing a U-turn to Water Street and thence to Madison Avenue). Access to the Port of Albany is made at Exit 2 (NY 32), to the south of the photo.
From southbound I-787, Exit 3A is for US 9 south and US 20 east to Rensselaer, and the Empire Plaza. Exit 3B is for US 20 west (via Madison Avenue) and the Port of Albany. Access to US 9 north is made at Exit 4B, to the north of the photo (Exit 4A, still farther north, is for Colonie and Columbia Streets, via Water Street at its northern end).
The interchange: The most striking feature of this interchange is the double circle of flyover ramps, which affords a full connection between I-787, US 9 north and south, US 20 east, and the South Mall Expressway west to the Empire State Plaza. Notice that in each of the freeway connections, the exit is to the right via a ramp which then splits to serve the two directions (this configuration is referred to as semi-directional). The ramps to and from the north have further splits, providing access to and from either I-787 (the mainline) or US 9 (the service roads). Although from above, these ramps do form a perfect circle formation, they appear from the ground as nothing more orderly than a complex, spidery jumble of overpasses.
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Photo by Christopher Jordan
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At the bottom level, entirely within yet completely independent of the circle interchange, Exit 4 from northbound I-787 and Exit 3B from southbound I-787, along with their corresponding entrance ramps, form a complete "diamond" interchange. (The northbound entrance ramp is largely obscured in this photo by the elevated ramps.) This diamond interchange lies within the median of what is functionally a two-way, divided local street, comprising Quay Street northbound and Church Street southbound (the southward continuation of Water Street). The southbound on and off ramps meet Church Street in such a way as to from a crossroads with Madison Avenue, which leads after two blocks to NY 32 and US 20. Immediately north and south of the diamond interchange are underpasses connecting the service roads, resulting in full access to and from both north and south, as well as west, from any of the four ramps of the diamond.
Rensselaer connections: Across the Hudson River, in Rensselaer, the Dunn Memorial Bridge has an obvious stub end. This was intended to carry the South Mall Expressway through Rensselaer, connecting to the east with I-90 at Exit 8. Today, Exit 8 serves the new extension of NY 43, but previously there had been stub ramps at this location for the never-built expressway. Through traffic for US 9 and US 20 at the east end of the bridge comes on and off by way of two tightly curved ramps. These become a connecting roadway running parallel to, and one block west of, Broadway (not to be confused with Broadway in Albany across the river) before turning southeast onto Columbia Street (not visible here).
An exit ramp from the US 9/US 20 connector branches off, forming a full 390-degree loop. This intersects Broadway, serving downtown Rensselaer and the Amtrak station, as well as NY 151. NY 151 (Third Avenue) intersects Broadway directly opposite another ramp, this one an entrance to US 9 and US 20. This, the westernmost end of NY 151, was formerly part of NY 43 before the latter's extension to I-90 was built. Originally, NY 43 also crossed the bridge into Albany and continued beyond on what is now NY 443.
US 20 west connection: Immediately to the west of the circle interchange is another diamond interchange with NY 32 (South Pearl Street), just south of the Pepsi Arena. The eastern half of the diamond carries through traffic for US 20 (westbound traffic exits the freeway here; eastbound traffic enters). The westbound on-ramp intersects Grand Street, which crosses under the South Mall Expressway one block west of South Pearl Street. US 20 traffic used to follow Grand Street instead of South Pearl Street for its one block connection between Madison Avenue and the expressway. This was recently changed, and the one block section of Grand Street is today reference route 912G. This same ramp also provides access to Eagle Street northbound, at top left. The former eastbound exit ramp to South Pearl Street was reconfigured to allow access to a parking garage on the south side of the expressway. At the same time, the split between the US 20 and I-787 approaches was moved westward to eliminate the possibility of weaving movements between the garage and the Dunn Memorial Bridge.
Notice how the US 20 ramps slip inside of the ramps for the circle interchange. The practical result of this is that US 20 westbound is unavailable directly from I-787, which is similarly unavailable from US 20 eastbound. This is why Exit 4 northbound and Exit 3B southbound are signed for US 20 west. Another result of this arrangement is a spectacular demonstration of the ability of highway engineering to be beautiful and graceful, at least from above. (For a view of this area from below, click here.) In fact, this entire interchange complex, besides being a feat of civil engineering, is a paragon of utility, simplicity (a full set of connections is available with a minimun number of ramps) and symmetry, yet also of power and dignity. It is fitting both from its design and its location at the heart of New York's capital, that this interchange be considered the flagship of the Empire State's highway system.
