Odd Interchange at the Tappan Zee

[Roadsguy]

I noticed that the interchange with US 9W at the western end of the Tappan Zee Bridge is very overkill (even though it's really twisty ). Though US 9W south of here is only two lanes, one ramp bridge crossing 287/87 is three lanes wide, and wide enough for four. Another bridge is two lanes and wide enough for three. Was there supposed to be an expressway ending here?

And why is there no eastbound (southbound?) off-ramp?

[NE2]

A lot of it can be explained by the topography, lying at the foot of a cliff.
http://mapper.acme.com/?ll=41.08084,-73.92215&z=15&t=T

[Roadsguy]

Well, that answers the far smaller part of my question.

EDIT: How old is that topo map you linked me to? The expressway east of the bridge was probably eight-laned recently, but was the bridge once only six lanes? I figured it would have once been eight (narrow) lanes like the Walt Whitman or Ben Franklin in Philly.

SUB-EDIT: Man, looking around, it shows NY 9A as being I-478 (it's not even an expressway there!) and the one-direction NY/I-878 expressway as not being finished yet!

[NE2]

Search here for Nyack: http://nationalmap.gov/historical/
Presumably that's the 1979 topo (original 1967). Note that I-87 is not marked on the Thruway, since in 1967 I-87 was over on current I-684.

[Henry]

Judging from the topography alone, it would be very expensive to rebuild the interchange, and with the presence of the cliffs, I don't think it's even worth the risk.

[connroadgeek]

Don't see why a diamond interchange wouldn't work there. It does seem like overkill, and the cliff has little to do with it as it seems there is plenty of space there. I mean if they built *that* interchange, they could build just about any interchange in that space. Perhaps I just don't understand the capacity requirements for a 9W to 287 interchange.

[Roadsguy]

I think I figured it out myself.

New Jersey Turnpike Northern Extension!

It would probably have been mostly used as a through-traffic bypass of NYC, maybe all as an I-95 3di. It's also probably why the overpowered ramps all point eastbound across the bridge, not west/northbound on 287/87.

[Kacie Jane]

Not as I'm reading it.

In 1960, the Rockland County Planning Department recommended that the proposed New Jersey Turnpike Extension follow an alignment parallel to NY 303 and the CSX (Conrail) River Line. To insure controlled access, interchanges were to be placed only at the Palisades Interstate Parkway in Orangeburg, and at the New York State Thruway in West Nyack. A new EXIT 12A was to be constructed on the thruway mainline for the New Jersey Turnpike extension.

The extension would have been well west of here.  Because of the cliffs, there's no room for a north-south expressway here, which is presumably why the PIP veers northwest at the state line.

Personally, I don't see any of these ramps as being overpowered.  I don't see any three-lane ramps.  Each of the circular ramps crossing over the Thruway are two lanes presumably to prevent people from having to merge/change lanes while going around the curves.  The inner ramp splits between 9W SB and NB on the west side of the Thruway, and the outer ramp has a merge immediately east of the Thruway.  (Short version:  I think it's "overpowered" for safety reasons.)

[Roadsguy]

Not as I'm reading it.

In 1960, the Rockland County Planning Department recommended that the proposed New Jersey Turnpike Extension follow an alignment parallel to NY 303 and the CSX (Conrail) River Line. To insure controlled access, interchanges were to be placed only at the Palisades Interstate Parkway in Orangeburg, and at the New York State Thruway in West Nyack. A new EXIT 12A was to be constructed on the thruway mainline for the New Jersey Turnpike extension.

The extension would have been well west of here.  Because of the cliffs, there's no room for a north-south expressway here, which is presumably why the PIP veers northwest at the state line.

Personally, I don't see any of these ramps as being overpowered.  I don't see any three-lane ramps.  Each of the circular ramps crossing over the Thruway are two lanes presumably to prevent people from having to merge/change lanes while going around the curves.  The inner ramp splits between 9W SB and NB on the west side of the Thruway, and the outer ramp has a merge immediately east of the Thruway.  (Short version:  I think it's "overpowered" for safety reasons.)

Some of the bridges are wider than the lanes they carry, as if they were built in anticipation to widening.

[empirestate]

And why is there no eastbound (southbound?) off-ramp?

I don't know the history of this interchange, but there's clearly provision for that missing ramp. There's that extra width on the NB-to-SB ramp (the 2-lanes wide enough for 3), and if you look closely, the retaining wall is squared off adjacent to the SB Thruway (it's more apparent in older aerials where there's less overgrowth: http://www.empirestateroads.com/week/i87-i287-us9w-2004-full.jpg). That's where the SB offramp would have joined. Also, the helix overpass just north of there has empty space for the offramp: there's an extra girder span on its west end rather than a wingwall.

As for the 3-lanes wide enough for 4 bridge (the southernmost), the extra space there is actually a separate span for the old Erie Railroad, now a rail trail. So while I'd agree that they do seem to have left some room for expansion, I don't think it ever went beyond just the missing SB ramp.

[Alps]

The ramps are wide in part because of the curvature. The bridge started as 6 lanes with a median shoulder, before that was converted to a reversible lane.