Does the Weehawken helix have any purpose?

[zzomtceo]

It always seemed quite useless to me. For anyone wondering it is the loop in SR 435 495 in New Jersey right before the Lincoln tunnel to Manhattan.

[hotdogPi]

You mean 495, not 435, right?

[zzomtceo]

You mean 495, not 435, right?

Yes, sorry

[TXtoNJ]

It always seemed quite useless to me. For anyone wondering it is the loop in SR 435 495 in New Jersey right before the Lincoln tunnel to Manhattan.

Have you been there? The surrounding topography makes the purpose of the helix very clear.

[zzomtceo]

It always seemed quite useless to me. For anyone wondering it is the loop in SR 435 495 in New Jersey right before the Lincoln tunnel to Manhattan.

Have you been there? The surrounding topography makes the purpose of the helix very clear.

I have not, it just looked weird on a map. Could you explain it?

[NE2]

Have you been there? The surrounding topography makes the purpose of the helix very clear.

I have not, it just looked weird on a map. Could you explain it?

http://mapper.acme.com/?ll=40.77004,-74.02631&z=15&t=T
The Palisades are about 200 feet above sea level. Even though NJ 495 is depressed under cross streets, that's at most 20 feet or so, meaning it has to get down about 150 feet in 1/4 mile, a dangerous 11% grade. The only way to ease the grade without starting the decline farther west (requiring more digging in the Palisades rock) is to add a hairpin or helix (mountain railroads are full of both because the standard maximum grade is 2.2%, as opposed to 6% on Interstates). The actual grade on the helix is something like 3-4%.

Compare this to adjacent crossings:
The Amtrak tunnel just to the south goes completely through the Palisades. A six-lane highway tunnel would be much wider and would require ventilation (the rail tunnel has been electrified since it opened).
At the Holland Tunnel, the Palisades are lower (less than 100 feet) and farther from the river, causing no problem in getting from the depressed Route 139 to the surface-level 12th and 14th Streets.
The George Washington Bridge is, of course, a bridge, so it doesn't need to get down to below sea level from the Palisades (here about 300 feet tall). It's interesting to note that the lower level approaches actually have short tunnels, as the bridge surface level is slightly below the top of the Palisades. (Here Manhattan has its own hill, which is about 150 feet above sea level.)

[roadman]

The other thing noteworthy about the rail tunnel is that, although most of the Northeast Corridor line across New Jersey is four tracks, there are only two tracks under the Hudson River (one in each tube).

[cl94]

The other thing noteworthy about the rail tunnel is that, although most of the Northeast Corridor line across New Jersey is four tracks, there are only two tracks under the Hudson River (one in each tube).

Hence why they want to build two more tubes. The current ones were badly damaged by Sandy and they can't fix them without closing a track completely.

[NE2]

The other thing noteworthy about the rail tunnel is that, although most of the Northeast Corridor line across New Jersey is four tracks, there are only two tracks under the Hudson River (one in each tube).

Part of the reason is that the line splits at Kearny, with many commuter trains going instead to Jersey City (and a PATH/ferry transfer).

The East River tunnel has four tracks, in part because New Jersey trains run through to Queens to turn around. Long Island City serves the same purpose as Jersey City for some local trains.

[Pete from Boston]

The other thing noteworthy about the rail tunnel is that, although most of the Northeast Corridor line across New Jersey is four tracks, there are only two tracks under the Hudson River (one in each tube).

Part of the reason is that the line splits at Kearny, with many commuter trains going instead to Jersey City (and a PATH/ferry transfer).

The East River tunnel has four tracks, in part because New Jersey trains run through to Queens to turn around. Long Island City serves the same purpose as Jersey City for some local trains.

You've lost me.  The Pennsylvania had terminal at Jersey City (the pre-1910 terminus of today's Northeast Corridor in New Jersey) but it and the tracks to it were demolished decades ago.  There is no surface heavy passenger rail service there anymore. 

The Erie and Lackawanna trains from the north and west go to Hoboken, immediately north of JC (Erie's Pavonia terminal in JC having also been demolished many years ago).  Since all passenger service in the state became NJTransit these systems have been interconnected, I think in Kearny, which sounds something like what you're talking about.

[NE2]

You've lost me.  The Pennsylvania had terminal at Jersey City (the pre-1910 terminus of today's Northeast Corridor in New Jersey) but it and the tracks to it were demolished decades ago.  There is no surface heavy passenger rail service there anymore.

Oops - I had Jersey City and Hoboken confused (the Hoboken station is just barely north of the Jersey City line). But the idea is the same: some ex-PRR commuter trains turn off at Kearny to use the ex-Lackawanna to Hoboken. (However, a bunch of trains from the ex-Lackawanna lines go to Penn Station using a similar connection, so there are probably at least as many trains on the two-track tunnel as on the four-track NEC south of Kearny.)

[bzakharin]

You've lost me.  The Pennsylvania had terminal at Jersey City (the pre-1910 terminus of today's Northeast Corridor in New Jersey) but it and the tracks to it were demolished decades ago.  There is no surface heavy passenger rail service there anymore.

Oops - I had Jersey City and Hoboken confused (the Hoboken station is just barely north of the Jersey City line). But the idea is the same: some ex-PRR commuter trains turn off at Kearny to use the ex-Lackawanna to Hoboken. (However, a bunch of trains from the ex-Lackawanna lines go to Penn Station using a similar connection, so there are probably at least as many trains on the two-track tunnel as on the four-track NEC south of Kearny.)

There are exactly 5 trains from south of Kearny that go to Hoboken (and vice versa) on weekdays. There are 50 Midtown Direct trains from the ex-Lackawanna lines using the tunnels into New York.