What is the mysterious fourth rail for?

March 23, 2007 12:33 PM

I'm relatively new to New York and ride the subway every day. When I'm on the above-ground lines I notice another "fourth" rail in between the two running rails that doesn't look like it is used, but is securely tied down. Sometimes there's even a fifth rail, also in the middle. Usually this rail doesn't run continuously and it occasionally curves or has other oddities. What is this fourth rail for?

Here's a picture. I know it isn't the third rail.

posted by pithy comment to Travel & Transportation (15 answers total)

I don't know for sure, but I've assumed that those are spare parts. Storage-in-place for efficient rail replacement.
posted by o2b at 12:37 PM on March 23, 2007

Could it from when the subway lines were independently owned, presumably before the car types were standardized? Older cars may have had a wider wheel base.
posted by skwm at 12:38 PM on March 23, 2007

There are two standard train widths. Those rails may be because the cleaning trains are still in use may use the smaller track size. Or perhaps it was just not worth it to rip out the middle rail when they renovated.

Or perhaps certain parts of the tracks have newer trains, with newer rails. They keep the old size in case they need to place one of the older trains in there.
posted by markovich at 12:42 PM on March 23, 2007

Response by poster: I thought it might be storage-in-pace, but it seems odd that it is so well tied down then. one or two spikes would hold the rail steady instead of one on every railroad tie.
posted by pithy comment at 12:43 PM on March 23, 2007

You might really enjoy this.
posted by phaedon at 12:43 PM on March 23, 2007

Best answer: The extra rail is a safety feature. If the train derails, the wheels fall off the regular rails. Depending on the momentum, the train can move pretty far sideways before coming to a full stop. This would be very bad on an elevated structure or a bridge, because the train could fall off the bridge as well as falling off the rails.

The extra pieces of rail are installed to catch the trailing-side wheels in the event of derailment to prevent the falling-off-the-bridge scenario. You can see them on regular train tracks too, but only on overpasses or bridges or places where derailment would be extra icky.

They have a name, maybe derailers or rerailers, but I'm not sure, and my train-loving mother isn't sure either.
posted by janell at 12:59 PM on March 23, 2007

They're guard rails, used on bridges and trestles -- janell got it (and the reason for them) right; the rest of you are just guessing.
posted by mcwetboy at 1:16 PM on March 23, 2007

the rest of you are just guessing

Pffft... that never stops anyone here...
posted by mkultra at 1:56 PM on March 23, 2007 [1 favorite]

Yup, 3rding the guard rail. They were invented as the result of a train accident where a train derailed as it hit the bridge, which moved mass over parts of the bridge which were not designed to handle the weight. Subsequently the bridge failed, and a big portion of the train fell into the water. If these protective 'guide rails' had been installed, many lives would have been saved. Every rail bridge now has these, usually there are a pair of rails installed parallell to the running track, on the inside of the regular rails. I can't seem to find the details of this original accident right now though..
posted by defcom1 at 2:15 PM on March 23, 2007

Sorry, I'm with the guesses.. Guard rails look like this. See how close they are to the actual running rails - only a few inches of clearance. The extra rails in the picture are 6"-12" away from the main rail. Also, I've seen similar in Toronto on subway tracks that are in an open cut, below grade.

It looks much more like severely disused dual gauge track to me..

Still just superficial guesswork though..
posted by Chuckles at 3:33 PM on March 23, 2007

It's not dual gauge. The various systems that connected together to form the NY subway system always ran standard gauge trains on the subway. Very old historical trains still make special trips on the tracks!
posted by Geckwoistmeinauto at 3:52 PM on March 23, 2007 [1 favorite]

Chuckles: You linked to a whole Google Images search page there, but the train-related pictures that did show up were of guard rails at switches, which are different from these ones.
posted by mendel at 4:11 PM on March 23, 2007

phaedon: You might really enjoy this.

Here's a version with pictures.
posted by bshort at 4:25 PM on March 23, 2007

Uh, I thought the IRT ran a different gauge than BMT and IND. Maybe it's just the bodies that are a different size.. I'm sure the answer is somewhere on nycsubway.org. ;)
posted by wierdo at 11:18 PM on March 23, 2007

I've dug up some more visual evidence.. Here are a bunch of guard rails.

So I can see that it does look like a guard rail, especially because of the way it is spiked, which is very similar to some of the photos I linked. However, it is only on one side, unlike all the other examples I found.

OK, I get it now.. They aren't guarding against falling off a bridge, they are guarding against encroachment onto the oncoming tracks!
posted by Chuckles at 10:57 AM on March 24, 2007