Subway Weight Issues on Manhattan Bridge, but not on Ben Franklin

[roadman65]

Was reading how NYC has to deal with the Subway Trains damaging the Manhattan Bridge in their city because of its design flaw of placing the four Subway tracks on the outside of the deck instead of in the middle.

Yet further south in Canden and Philadelphia,the Ben Franklin Bridge has the same set up, but their Bridge dont develop structural issues like the Manhattan Bridge does causing the roadway to twist up to 8 feet into the direction of the train's weight.

Both bridges are suspended from cables and both have the heavy trains using the outer part of the deck.  Yet one has problems, but the other don't.  Makes me wonder what did engineers do when building the Manhattan Bridge that was wrong if those building the Ben Franklin Bridge got it right.

[Beltway]

The Manhattan Bridge twists because its original stiffening truss was too flexible, and NYC runs long trains constantly on the outer tracks, creating huge torsional loads. The Ben Franklin Bridge has a much stiffer truss and carries shorter, less frequent trains, so it doesn't develop the same problems.

The Manhattan Bridge's four‑track layout exists because NYC needed express and local service with extremely high frequency. That operating pattern creates far more load cycles than the Ben Franklin Bridge ever sees, which is why one bridge twists and the other doesn't.

[1995hoo]

The Manhattan Bridge's four tracks aren't the same as the local/express configuration throughout much of the New York subway. There are two tracks on each side of the bridge and they connect to different lines at each end, rather than all four going to the same place. With the current configuration, the local trains for the Broadway Line (the south side of the bridge) use the Montague Street Tunnel and go along the western edge of the Financial District, while the express trains cross the bridge. Similarly, the local trains for the Sixth Avenue Line (the north side of the bridge) use the Rutgers Street Tunnel and the express trains use the bridge.

In the past, the south side of the bridge was connected to the Nassau Street Loop (the southern end of what is now the J/Z trains). Trains coming from Brooklyn would either go through the Montague Street Tunnel, go around the loop, and cross the bridge back to Brooklyn, or go across the bridge, go around the loop, and return to Brooklyn via the tunnel. The north side tracks connected to the Broadway Line at the Canal Street stop. That all changed in 1967. The Nassau Street Loop was severed, the south tracks were rerouted to the Broadway Line, and the north tracks were connected to the Sixth Avenue Line.

Historically the Broadway Line tracks carried much heavier service loads than the Nassau Street Loop did, which led to the north side of the bridge suffering much greater loads and experiencing considerably more twisting and other structural abuse than the south side did. Nowadays the north side still carries more traffic because the N runs local through the tunnel overnight instead of using the bridge (the Q still runs), while the B and the D maintain overnight service.

[Beltway]

I stand corrected then. But with two separate 2-track rapid rail lines that is still double the trackage of the Ben Franklin. It being NYC and Lower Manhattan they both would carry far more cars per day than the PATCO line.

[1995hoo]

I stand corrected then. But with two separate 2-track rapid rail lines that is still double the trackage of the Ben Franklin. It being NYC and Lower Manhattan they both would carry far more cars per day than the PATCO line.

Definitely. And the tracks probably should have been put in the center with the roadways on the outside.

There is a pedestrian walkway on the south side of the Manhattan Bridge. It must be incredibly loud when the train goes by.

[Dirt Roads]

The Manhattan Bridge twists because its original stiffening truss was too flexible, and NYC runs long trains constantly on the outer tracks, creating huge torsional loads. The Ben Franklin Bridge has a much stiffer truss and carries shorter, less frequent trains, so it doesn't develop the same problems.

The Manhattan Bridge's four‑track layout exists because NYC needed express and local service with extremely high frequency. That operating pattern creates far more load cycles than the Ben Franklin Bridge ever sees, which is why one bridge twists and the other doesn't.

I stand corrected then. But with two separate 2-track rapid rail lines that is still double the trackage of the Ben Franklin. It being NYC and Lower Manhattan they both would carry far more cars per day than the PATCO line.

My understanding is that there is twisting, which is indeed due to the use of Warren truss structure (the Manhattan Bridge was actually the first suspension bridge to ever utilize a Warren truss deck support). 

Since most Warren truss designs don't have any vertical elements, both twisting and frequency resonance can occur and need to be isolated (ergo, stiffened) by the installation of vertical struts in certain places.  That is perceived as "architecturally ugly", so most bridges are not stiffened which results in the affected diagonal struts needing to be replaced more frequently.  The Manhattan Bridge opened in 1909 and was first renovated starting November 1979 (70 years, as opposed to 100-year design life), construction not completed until February 2004; and the most recent renovation starting November 2018 (109 years, perhaps a few elements being replaced at 40 years or so), so in the grander scheme of things those problems aren't really all that bad.  (Thus, both <beltway> and <1995hoo> have made valid points).

Historically, the tracks on the north side of the Manhattan Bridge connected to the heavily-utilized BMT Broadway Line, whereas the tracks on the south side of the bridge connected to lesser-utilized BMT Nassau Street Loop.  The latter service was severed in 1967, leaving the south side of the bridge with BMT 4th Avenue Line and BMT Brighton Line trains (perhaps even more lopsided).  This imbalance of trains has led to what the MTA calls "flexing" of the entire bridge structure.  That is combined with the fact that subway cars naturally exhibit low-frequency vibration patterns on the tracks and substructures (oftentimes in the audio frequency range, hence the loud noises as compared to freight railcars or semi-trucks). 

It is my understanding that the imbalance of subway services was envisioned during the original design (and redesigns) of the Manhattan Bridge.  But the inherent differences between wooden subway cars and modern-day subway cars are still requiring the Manhattan Bridge to be repaired frequently.  There have been several proposals to balance the subway traffic between the north side and the south side of the bridge, but alas it is still much much less expensive to keep fixing the bridge.

[For the record, I've worked on vibration issues for bridge structures related to medium-sized passenger cars exhibiting ultra-low frequency vibrations (such as magnetic-levitation and air-levitation trains).  That is a whole different can of worms, and I'm not very knowledgable about this structural area other than having worked on most of the subway lines in Brooklyn].

[Beltway]

Historically, the tracks on the north side of the Manhattan Bridge connected to the heavily-utilized BMT Broadway Line, whereas the tracks on the south side of the bridge connected to lesser-utilized BMT Nassau Street Loop.  The latter service was severed in 1967, leaving the south side of the bridge with BMT 4th Avenue Line and BMT Brighton Line trains (perhaps even more lopsided).  This imbalance of trains has led to what the MTA calls "flexing" of the entire bridge structure.  That is combined with the fact that subway cars naturally exhibit low-frequency vibration patterns on the tracks and substructures (oftentimes in the audio frequency range, hence the loud noises as compared to freight railcars or semi-trucks). 

What would be involved in reconfiguring the lines so that the outer tracks would be one subway line and the inner tracks would the other subway line? That would always keep things in balance even after changes in frequency over time.

[1995hoo]

Historically, the tracks on the north side of the Manhattan Bridge connected to the heavily-utilized BMT Broadway Line, whereas the tracks on the south side of the bridge connected to lesser-utilized BMT Nassau Street Loop.  The latter service was severed in 1967, leaving the south side of the bridge with BMT 4th Avenue Line and BMT Brighton Line trains (perhaps even more lopsided).  This imbalance of trains has led to what the MTA calls "flexing" of the entire bridge structure.  That is combined with the fact that subway cars naturally exhibit low-frequency vibration patterns on the tracks and substructures (oftentimes in the audio frequency range, hence the loud noises as compared to freight railcars or semi-trucks). 

What would be involved in reconfiguring the lines so that the outer tracks would be one subway line and the inner tracks would the other subway line? That would always keep things in balance even after changes in frequency over time.

In order to avoid disrupting service when trains crossed at-grade, they'd have to reconfigure the tracks. See diagram below from NYCSubway.org. They'd have to connect both "outer" tracks to the Broadway Line and both "inner" tracks to the Sixth Avenue Line. I have no idea whether that is possible, much less practical, for the outer track on the north side of the bridge and the inner track on the south side. Certainly the north side tracks did connect to the Broadway Line until 1967, but whether it's possible to reconnect them, much less with a "split-level" configuration to let the tracks cross over at different levels, is just something about which I have no idea.

On the Brooklyn side, they'd probably have to install a switch somewhere between the bridge and the area of the abandoned Myrtle Avenue station to allow a train from the inner track to cross over to the outer track. That side would be a lot less complicated in that respect. There is presently no such connection. Presumably it could be done, similar to how the local trains on the Fulton Street Line use a switch to move to and from the express tracks near Hoyt–Schermerhorn Streets.

Here is the source page for the track maps. Good resource if you're interested in this sort of thing: https://www.nycsubway.org/wiki/New_York_City_Subway_Track_Maps (There used to be a WMATA "schematic" diagram online from John Cambron. I don't know whether it's still online. I think I have it saved somewhere, but it would require searching.)

[Dirt Roads]

Historically, the tracks on the north side of the Manhattan Bridge connected to the heavily-utilized BMT Broadway Line, whereas the tracks on the south side of the bridge connected to lesser-utilized BMT Nassau Street Loop.  The latter service was severed in 1967, leaving the south side of the bridge with BMT 4th Avenue Line and BMT Brighton Line trains (perhaps even more lopsided).  This imbalance of trains has led to what the MTA calls "flexing" of the entire bridge structure.  That is combined with the fact that subway cars naturally exhibit low-frequency vibration patterns on the tracks and substructures (oftentimes in the audio frequency range, hence the loud noises as compared to freight railcars or semi-trucks). 

What would be involved in reconfiguring the lines so that the outer tracks would be one subway line and the inner tracks would the other subway line? That would always keep things in balance even after changes in frequency over time.

In order to avoid disrupting service when trains crossed at-grade, they'd have to reconfigure the tracks. See diagram below from NYCSubway.org. They'd have to connect both "outer" tracks to the Broadway Line and both "inner" tracks to the Sixth Avenue Line. I have no idea whether that is possible, much less practical, for the outer track on the north side of the bridge and the inner track on the south side. Certainly the north side tracks did connect to the Broadway Line until 1967, but whether it's possible to reconnect them, much less with a "split-level" configuration to let the tracks cross over at different levels, is just something about which I have no idea.

On the Brooklyn side, they'd probably have to install a switch somewhere between the bridge and the area of the abandoned Myrtle Avenue station to allow a train from the inner track to cross over to the outer track. That side would be a lot less complicated in that respect. There is presently no such connection. Presumably it could be done, similar to how the local trains on the Fulton Street Line use a switch to move to and from the express tracks near Hoyt–Schermerhorn Streets.

The ultimate goal would be completion of the IND Second Avenue subway (Q-train, south side of the bridge), which would take significant numbers of passengers off of the IND Sixth Avenue Line (B-train and D-train, north side of the bridge).  At one time, NYCT was projecting that the Second Avenue Line would actually overtake the Sixth Avenue Line in terms of passengers during the "rush hour" (which is way longer than an hour).  But keep in mind that the Manhattan Bridge was actually designed with the expectation that the subway traffic on the north side of the bridge would be much heavier than on the south side of the bridge (how they could possibly expected that back in 1901 when they had wooden railcars is beyond my comprehension).

So let's say that 25 years from now, the IND Second Avenue Line is finally completed and subway traffic over the Manhattan Bridge is then nearly balanced between the north side and the south side.  I highly suspect that there would be some major changes needed, after generations of "stiffening" efforts (unbeknownst to us common folks) that have addressed the current "flexing" issues.  It's pretty cool to think of a bridge structure that has likely "morphed" many times over its 117-year life.

[Dirt Roads]

Not sure if <roadman65> wanted any comparisons, but the Ben Franklin was constructed with wide-gage streetcar tracks that were installed down the middle of the bridge.  The streetcars never materialized and the rails were removed after the streetcar system abandoned its plans for a streetcar system in Camden.

The Ben Franklin was also constructed with provisions for one subway track on each side.  The Bridge Line subway (constructed by the South Jersey Transit Commission) was completed in 1936, and now has been reconfigured for use by the PATCO Speedline (Lindenwold Line), which is not considered a subway system at the time but rather a railroad due to shared usage of freight lines somewhere on the Jersey side.  Traditionally, the PATCO passenger cars were much heavier than subway cars (similar to the PATH system operated by PANYNJ) that met FRA crashworthiness regulations.  From what I can tell, PATCO is no longer subject to Federal Railroad Administration (FRA) regulations.

[1995hoo]

... completion of the IND Second Avenue subway ...

It would be interesting to run that line past its planned terminus at Hanover Square through a new tunnel to Court Street in Brooklyn, connecting it to the Fulton Street Line. Won't ever happen, of course, and would be astronomically expensive; it'd also result in the demise of the Transit Museum (which is in the Court Street station) unless they were to rehabilitate some other disused station for that purpose (but the problem there is that just about every other one is on active tracks). I also tend to think it would not be an especially popular service because it would connect to the local tracks on the Brooklyn side. The Second Avenue Line is only two tracks, so that would make for some long rides.

I certainly don't expect to see the Second Avenue Line reach the Financial District in my lifetime (I'm in my 50s).

[Beltway]

It would probably take some major construction at each end of the bridge to interleave the tracks with grade separation to do what I suggested, and part of that underground. So it may be more difficult than any benefits.

[Henry]

Philly is not very well-known for its subway system like NYC is (nor is any other city, though DC comes closest to rivaling it), so my guess is that the builders of the Ben Franklin Bridge studied the flaws in the Manhattan Bridge and made substantial improvements to ensure a safer crossing for all.

[Dirt Roads]

... completion of the IND Second Avenue subway ...

It would be interesting to run that line past its planned terminus at Hanover Square through a new tunnel to Court Street in Brooklyn, connecting it to the Fulton Street Line. Won't ever happen, of course, and would be astronomically expensive; it'd also result in the demise of the Transit Museum (which is in the Court Street station) unless they were to rehabilitate some other disused station for that purpose (but the problem there is that just about every other one is on active tracks). I also tend to think it would not be an especially popular service because it would connect to the local tracks on the Brooklyn side. The Second Avenue Line is only two tracks, so that would make for some long rides.

I certainly don't expect to see the Second Avenue Line reach the Financial District in my lifetime (I'm in my 50s).

Keep in mind that the current IND Second Avenue subway (Q-train) is already connected to the south side of the Manhattan Bridge.  The Hanover Square terminus would be for other trains (which might also end up with the Q-train moniker, given that NYCT is running out of letters).  (When I worked there, the Q-train ran up the IND Sixth Avenue Line).  It's just a matter of connecting a sufficient number of stations along the east side of Manhattan to populate a sufficient number of trains to balance the train loading over the bridge.  (More discussion later).

[1995hoo]

They've said the dedicated Second Avenue trains will be the T and will have a teal color on the map (similar to, but a slightly different color from, the late JFK Express). That could change, of course.

[1995hoo]

... (There used to be a WMATA "schematic" diagram online from John Cambron. I don't know whether it's still online. I think I have it saved somewhere, but it would require searching.)

...

I mentioned the above and I just found it online, so while it's not directly related to this thread, I figured I ought to post the link.

https://cambronj.blogspot.com/2020/12/wmata-129-mile-system-track-map.html

[Max Rockatansky]

You folks shouldn't make fun of a bridge over weight issues. 

[hotdogPi]

You folks shouldn't make fun of a bridge over weight issues. 

Relevant thread: https://www.aaroads.com/forum/index.php?topic=34241.0

[Max Rockatansky]

You folks shouldn't make fun of a bridge over weight issues. 

Relevant thread: https://www.aaroads.com/forum/index.php?topic=34241.0

Hey, I'd consider dating a bridge that was a little on the hefty side.

[kalvado]

You folks shouldn't make fun of a bridge over weight issues. 

Relevant thread: https://www.aaroads.com/forum/index.php?topic=34241.0

I was surprised no one mentioned dolphins there. They can make it fun!

[hotdogPi]

You folks shouldn't make fun of a bridge over weight issues. 

Relevant thread: https://www.aaroads.com/forum/index.php?topic=34241.0

I was surprised no one mentioned dolphins there. They can make it fun!

2023 was before the collapse.

[Dirt Roads]

... completion of the IND Second Avenue subway ...

It would be interesting to run that line past its planned terminus at Hanover Square through a new tunnel to Court Street in Brooklyn, connecting it to the Fulton Street Line. Won't ever happen, of course, and would be astronomically expensive; it'd also result in the demise of the Transit Museum (which is in the Court Street station) unless they were to rehabilitate some other disused station for that purpose (but the problem there is that just about every other one is on active tracks). I also tend to think it would not be an especially popular service because it would connect to the local tracks on the Brooklyn side. The Second Avenue Line is only two tracks, so that would make for some long rides.

I certainly don't expect to see the Second Avenue Line reach the Financial District in my lifetime (I'm in my 50s).

Keep in mind that the current IND Second Avenue subway (Q-train) is already connected to the south side of the Manhattan Bridge.  The Hanover Square terminus would be for other trains (which might also end up with the Q-train moniker, given that NYCT is running out of letters).  (When I worked there, the Q-train ran up the IND Sixth Avenue Line).  It's just a matter of connecting a sufficient number of stations along the east side of Manhattan to populate a sufficient number of trains to balance the train loading over the bridge.  (More discussion later).

They've said the dedicated Second Avenue trains will be the T and will have a teal color on the map (similar to, but a slightly different color from, the late JFK Express). That could change, of course.

It wasn't one of my MTA projects in NYC, but I was involved in some early discussions prior to the restart of the Second Avenue subway line.  One of the main issues was fleet allocation if/when the entire line gets constructed.  Back in the mid-1990s, the consensus was that many of the folks in Brooklyn that work on the east side of Manhattan would find a way to switch over to the Second Avenue Line (taking lots of passengers off of the IND Sixth Avenue Line and taking pressure off of the IRT Lexington Avenue line).  If so, the Second Avenue Line was going to need way more trains in the complete buildout than the IND Sixth Avenue Line.  (The trains down to Hanover Square add to the puzzle). 

I don't recall any discussion about how that would affect the balance of trains on the Manhattan Bridge, but I'd be surprised if there weren't such discussions at NYCT that the MTA folks weren't privileged to.

Everything that I've seen in the past showed plans for the Q-train coming off the Manhattan Bridge and running up the Second Avenue Line.  But the newer maps only indicate a transfer station to the B-train/D-train at Grand Street.  That throws everything about balancing trains over the Manhattan Bridge "down the tubes".  F-train, anyone?

[Max Rockatansky]

You folks shouldn't make fun of a bridge over weight issues. 

Relevant thread: https://www.aaroads.com/forum/index.php?topic=34241.0

I was surprised no one mentioned dolphins there. They can make it fun!

2023 was before the collapse.

Prior to the collapse of the Key Bridge or Beltway?