New Hudson Tunnels

Traditionally, proposals for new mainline rail tunnels across the Hudson enter Penn Station’s southern tracks, which are used by New Jersey Transit. This includes the ARC incarnations that connected to Penn Station’s preexisting tracks, Amtrak’s Gateway, and the Institute for Rational Urban Mobility’s through-running counter plan to ARC. To my knowledge, ARC-North proposals, entering the northern tracks used by the LIRR, have not been investigated. I am not ready to sign off on ARC-North yet and in fact called it a troll proposal, but I believe it deserves more study and is probably superior to southern proposals except at high levels of investment.

While this in principle only concerns the configuration of the tunnels across the Hudson, it has implications about the configuration of Penn itself and the service plan supported by the infrastructure. The one element of the various Penn Station redesign ideas that isn’t relevant is the look of the station itself; this is also the least important element for passenger throughput. Penn Station’s failure to look like a cathedral is a lesser problem in a city that is full of multi-billion dollar starchitect-designed ugliness.

First, some principles for tunnel design. A good infrastructure proposal should have the following elements:

1. A through-running service plan. It matters which line at the New Jersey (or Hudson Line) end connects to which line at the Long Island or Connecticut end, since this influences the interlockings. It also matters where people are expected to transfer, since this influences platform crowding; ideally, transfers should be handled at Secaucus and Sunnyside.

2. Simple interlockings. Complex interlockings limit train speed, and switches especially do. It should be possible for trains to enter and exit Penn Station at speed. Avoiding slow zones in station throats is an underrated way of improving line haul time at relatively low cost, and the fancier the trains and more upgraded the tracks elsewhere are, the heavier the time penalty of slow throats is.

3. Adequate platforms. Penn Station has less bad platforms than people think – when I timed rush-hour LIRR trains, they emptied in about 90 seconds or a little more – but they’re still not good, especially if we’re assuming large increases in ridership coming from better service. The LIRR has better platforms than New Jersey Transit because it has more access points per platform, but the platforms are still narrow. In the worst case, a plan should consider paving over some tracks to widen the platforms, since Penn’s 21 tracks are more than enough for its traffic.

4. Adequate speed for intercity trains. The current tunnels are limited to 60 miles per hour (97 km/h) because of air resistance generated by non-aerodynamic trains in narrow tunnels. The cross-sectional area of the trains going through the tunnels is about half the cross-sectional area of the tunnels; in new high-speed rail tunnels, the corresponding ratio, called the obstruction ratio, is about 15%. It is possible to squeeze more speed out of the existing tunnels with better aerodynamics and sealing, but 200 km/h is probably impossible, and even slightly lower speeds are a problem if the tunnels are very busy and there is a speed mismatch with unsealed, non-aerodynamic commuter trains. So ideally, the larger-diameter new tunnels should be used by intercity trains. We can plan around one minute of travel time difference; this figure can in reality be anywhere between zero and 2.5 minutes.

5. Separation between intercity trains and Grand Central trains. If there is a Penn-Grand Central tunnel, it should be used exclusively by commuter trains because of the high local travel demand, and because to reduce real estate acquisition cost the curve radius should be low, possibly too low for Shinkansen equipment. This means that if a Hudson tunnel points toward the Penn-Grand Central tunnel, intercity trains should use the other one.

6. Two platform tracks per tunnel track. This improves capacity in two ways. First, rapid transit capacity is a combination of tunnel capacity and station dwell, and splitting each tunnel track between two platform tracks allows slightly higher capacity by deemphasizing the dwell since successive trains use different platform tracks. Paris is limited to 30 tph on the RER A with moving-block signaling, whose central segment has one platform track per tunnel track, but the shared RER B+D tunnel between Gare du Nord and Chatelet-Les Halles gets 32 tph with fixed blocks, where the B and D serve separate platforms at each station. And second, because each train can dwell at the platform for longer, this reduces the need for wider platforms, allowing violations of #3. Ideally, the two platform tracks would face the same platform to improve wayfinding and allow unscheduled track changes in case of train delays.

Now, Penn’s tracks are numbered 1-21, from south to north. There are platforms between tracks 20-21, 18-19, 17-18, 15-16, 13-14, 11-12, 9-10, 7-8, 5-6, 3-4, and 1-2; the 18-19 platform is wider than the rest, as if there was supposed to be another track immediately north of 18. The Hudson tunnels connect to tracks 1-19, the southern pair of the East River tunnels connects to 5-15, the northern pair connects to 15-21. The Hudson tunnels and the southern pair face each other, and trains on tracks 11 and 12 go straight through every switch; the northern pair offers no switch-free option, since the eastbound track faces track 21 and the westbound curves into the interlocking.

Since the Hudson tunnels face the southern pair, a simple proposal for new Hudson tunnels should face the northern pair. This would give 4 tracks between New Jersey and Sunnyside. Each of the two track pairs could point toward either Long Island or Connecticut, because of the Harold Interlocking, flawed as it is. This means intercity trains would use the northern pair and go to Connecticut, other regional trains would use either pair and go to either Connecticut or Long Island, and Harold would be superfluous. New Penn-Grand Central tunnels could be constructed branching from the southern East River tunnel pair. It is possible to also construct the tunnels around the southern pair, with trains from the southern pair either merging heading into the Hudson tunnels or terminating and reversing at Penn Station.

Under this plan, all of the numbered principles could be satisfied except #3, and to satisfy #3 every plan requires track paving or other platform modification. It’s also simple to construct: it’s just a new tunnel pair, and ideally also some work on the preexisting southern East River tunnel pair to construct a connection to Grand Central. The one drawback is that, unlike in ARC Alt G, Gateway, and the IRUM plan, the Penn-Grand Central tunnel shares approach tracks to Penn Station with the southern tunnels, reducing capacity. This becomes a problem if ridership from Grand Central, the LIRR, and points east grows to the point of overwhelming three tunnel pairs (the two heading into Penn, and East Side Access). The alternative with the Penn-Grand Central tunnels going around the southern tunnel pair and only merging heading into the Hudson tunnels has more capacity, but interferes with principles #3 and #6.

Track-paving for any plan is hard, because many of the straightest, longest-platform tracks have to be removed. To widen the platforms and improve throughput, there are two ways to pave over tracks, each of which gets rid of about half the station tracks. One is to pave over every other track, guaranteeing each track access to two medium-width platforms; trains could open both doors then, improving egress. The other is to pave every other pair of adjacent tracks lying between platforms, giving each track access to just one very wide platform. The former option is difficult at Penn because there are support columns between adjacent tracks, and a look at New Jersey Transit rolling stock suggests that each train would have 1-2 doors facing a column. We are left with the latter option, paving over, for example, tracks 20, 17, 16, 13, 12, 9, and 8. Each tunnel track would get two platform tracks facing the same platform, except for the westbound northern tunnel track, whose two tracks (21 and 19) would be split because of the aforementioned columns. The lowest-numbered tracks would not be used; the LIRR’s West Side Yard would not be used regularly but instead trains would run on the tracks more often off-peak. The now enlarged platform between tracks 7 and 10 would be lengthened to allow 16-car trains at track 7, which is currently 13 cars long.

Since principles #3 and #6 are both satisfied, the capacity per track can be quite high. The RER B+D achieves 32 tph, but this is split as 20 tph B and 12 tph D, which is suboptimal since two successive trains could both be B, making the dwell a problem. With even alternation between each platform’s two tracks and moving-block signaling, even higher capacity may be possible, reducing the capacity disadvantage of having just two tunnels coming into Penn from the east rather than three.

The IRUM plan, building on ARC Alt G, is quire different. It has three tunnels in each direction: the northern East River tunnels are paired with the Hudson Line via a new short tunnel linking the Empire Connection with the northern Penn Station tracks, the new Hudson tunnels come into the southern station tracks and then continue to Grand Central via new tunnels, and no tracks are paved. Intercity trains have to keep using the old tunnels, necessitating Harold, but that’s money already spent. Principle #3 is violated, or alternatively #6 is if tracks are paved, but there is more track capacity. The risk there is insufficient demand from the Empire Connection, which would leave the northern tunnels underused, reducing the system’s capacity advantage over a two-tunnel option to just a few tph. This plan has to route intercity trains through the old tunnels. Conversely, the advantage is that it easily shoehorns Empire Connection service, which ARC-North does not.

The main difference between ARC-North and IRUM is investment levels. ARC-North is cheaper; it’s more comparable to the bare-bones proposals for ARC(-South) and Gateway that are hinted at but never formally published. At the low investment levels of a bare-bones proposal, ARC-North is superior because it provides better capacity because of the relatively straight train paths through the station. If there’s no connection to Grand Central, then it is not at a capacity disadvantage since Long Island and Connecticut don’t have the demand, and barely have the capacity, to overwhelm three track pairs (including East Side Access again).

Conversely, ARC-North is harder to retrofit for somewhat higher investment. The best that can be done is tunneling to connect the Empire Connection to the southern tracks, digging new tunnels to Long Island as in Alt S, and running trains to just one line, probably Lower Montauk, which goes through serviceable neighborhoods but lacks a direct connection to the existing tunnels to Penn. This provides much better service coverage because of the Montauk connection, but at higher cost since there’s an additional underwater tunnel. It avoids the expensive components of Gateway and ARC, but so does IRUM, which becomes an intermediate level of investment between ARC-North proper and ARC-North with a Montauk tunnel.


  1. PeakVT

    I have a map that captures (correctly, I hope) most of the options here.

    ARC-N seems to be the best option in a limited funding world. But IIRC the alignment was somehow vetoed by Weehawken, which is why ARC Alt-P made such a big dip to the south.

    • Nathanael

      “But IIRC the alignment was somehow vetoed by Weehawken,”
      I hadn’t heard that story. I would be interested.

      • PeakVT

        That may not be true, but I remember reading it somewhere (and of course I can’t figure out where now). It stuck in my mind because wtf is Weehawken?

        OTOH, the current Wikipedia article for ARC indicates there were multiple reasons, mostly related to limiting the grade to 2% into NYP. (An archived Railway Age article seems to be the source.) That’s probably a valid concern with current equipment. It also happens to be the ruling grade for the existing tunnels. One could argue that future equipment should be speced for higher acceleration, which would allow for higher grades in a new tunnel and (possibly) make the northern alignment viable again.

        I think the question for the project is how many permanent operational restrictions are we willing to impose. If it even gets built, a second set of Hudson tunnels stand a good chance of being the only one built for at least another century. The current mess hasn’t killed the city, but it’s clearly a limitation on transit access, which is much more important now than when the tunnels were originally built. So, should a different, though improved, mess be created, or should an extra effort be made to get the new tunnels as close to correct as possible? For better or worse, not it’s my call to make.

  2. jim

    I think it became clear with ARC that there isn’t going to be a Penn-GCT tunnel: the takings to implement one would be too large, the MTA isn’t willing to share GCT and there are real historic preservation issues raised by running through the food court. If there is ever to be a 31st St tunnel, it will run across the East River and connect to the Lower Montauk ROW as part of a NEC Second Spine effort. In which case the new Hudson tunnel should be to the south to connect with it.

    The LIRR operation is the least broken piece of Penn Station (at least at the platform level — there are considerable pax flow problems on the floor above). In the morning, trains come into their platform, unload quickly, the platform clears quickly, the train moves on to the West Side Yards and another train comes in. There’s little interference with other trains. What’s least broken shouldn’t be the highest priority to fix.

    An absolutely minimal Gateway is a single additional bore across the Hudson (plus a new Hackensack crossing and triple tracking into Dock East) into the A Yard. Any cut and cover west of Penn Station would be double tracked (while you’ve got the lid off you might as well put in two tracks), but the bored section would be single. Yes, the cost of a launch box, shafts and adits doesn’t vary much whether you’re boring one tunnel or two, but to bore, line, track, electrify and signal a single tunnel is about half the cost of boring, lining, tracking, electrifying and signaling two.

    In operation, the two existing North River Tunnels would carry traffic in the (NJ-NY) peak direction and the new tunnel would carry counterpeak traffic. NJT would have to identify storage space east of the Hudson for the bulk of its trains. All peak NJT traffic would run through, split between the two east river tunnels, to wherever it identified storage. NJT counterpeak would turn in Sunnyside, rather than at Penn. NJ-NY counterpeak traffic would use the southern East River tunnels, leaving the northern tunnels to LIRR. The stub tracks in Penn would be used by Amtrak Acela-branded New York-Washington (and possibly New York-Harrisburg) service, which would be cleaned and turned at the platform (these are short enough trips that the trains wouldn’t need inspecting, nor a crew change in NY: the turn comprises the Engineer walking the length of the platform and running a brake test). Possibly they would be lengthened to 400m. Metro-North would use tracks 5-8 as available for Hudson Line-New Haven Line run through.

    What would be needed to make this work would be a fairly thorough rebuilding of the two levels of Penn Station above the platform level. One doesn’t necessarily want a cathedral, but efficient, usable space doesn’t seem too much to ask for.

    And it does permit later expansion.

    • Adirondacker12800

      I think it became clear with ARC that there isn’t going to be a Penn-GCT tunnel

      They were going to build the stub ends on the eastern end of the platforms for the fun it?

    • Alon Levy

      This involves too many switching moves; the connections from the East River tunnels to the LIRR are such that this contraflow operation is difficult. If you have an eastbound a.m. LIRR train, it needs to cross opposing traffic at-grade as it heads into Sunnyside.

      I don’t believe the tunnel boring part of the operation is very expensive. The launch box is a much bigger component. In SAS, about three quarters of the cost is stations and only a quarter is the tunnels themselves. With today’s technology it’s not even that complex to tunnel underwater.

      • Adirondacker12800

        If you have an eastbound a.m. LIRR train, it needs to cross opposing traffic at-grade as it heads into Sunnyside.

        If the track maps that-are-no-longer-online are accurate, I assume they are since they were updated and revised thoroughly when they were online, both Eastbound tracks have grade separated access to Sunnyside. So do both Westbound tracks.

        • jim

          I think what Alon meant was that eastbound traffic from the southern tunnels currently has to cross eastbound traffic from the northern tunnels if it is to get to Hellgate or the Port Washington branch, so my idea of pushing NJT traffic across both tunnels would lead to conflict at those switches. It is, however, my understanding that the Harold Flyover project was intended to eliminate that conflict. It’s certainly possible I’ve misunderstood: at the time I joined in the chorus that condemned wasting HSIPR money on what appeared to be a commuter rail improvement and didn’t look very closely at precisely what was proposed.

          • Adirondacker12800

            Trains going to or from Port Washington or the Hells Gate Bridge aren’t going to Sunnyside.

    • Jonathan English

      I really don’t think the food court would need to be destroyed to extend the tracks south. The tracks are already on a lower level than the food court, and it seems as though they were designed to duck underneath if they were extended south.

  3. Henry

    Egress to and from LIRR platforms could be improved significantly without much widening of platforms if they would just remove escalators. As it stands, some of the platforms are connected to the concourse with a five-foot wide staircase and a two-foot wide escalator at the 7th Av ends. Since these are generally also the most congested exit points due to the proximity to the (2) and (3), these are a huge constraint on clearing out the platforms. Considering that the concourse is not that much higher than the platforms, the escalators could be ripped out and the stairs widened, providing better egress.

    The track configuration around Penn is weird – some of the platforms are narrow because tracks start converging before the platform ends, and there are a couple of switches past the start of the platforms.

    • Alon Levy

      It’s good at high levels of investment. At low ones, intended to four-track the Hudson tunnels but do nothing else, it’s not, because the obvious scaling down requires trains to make a lot of awkward switching moves at Penn.

  4. Charles Smith

    You mention tunnel cross-section to train cross-section ratios for various speed regimes, and suggest knowledge of other factors impacting train speeds in tunnels. I’ve had limited success finding references about this and would welcome any that you can share please.

    • Richard Mlynarik

      I’ve found that there is in fact a large amount of information out there. is a good start.
      If you have access (this stuff is never open access, sigh) to an university engineering library, I’ve found plenty in aerodynamics/CFD journals and proceedings.
      Much is biased towards high speed trains, but there’s plenty of useful info.

      In practice, the most useful information is to look at the designs of contemporary European tunnels (my Google-fu is at 0% for Asia, sadly) and see what they do. There have been a large number of S-Bahn-ish cross-city projects over the last decade (München, Stockholm, Leipzig, Zürich, Milano, Madrid, Barcelona, Malmö, London, Oslo, etc etc), with numerous others on the drawing boards, and cross-sections and longitudinal plans (evacuation, ventilation, etc) can be dug up. Just a few strategic keywords (eg “Querschnitt” in German) make a useful start.

      As always, for most of this stuff one doesn’t need to understand profoundly, except to know that copying people who do know what they’re doing is the only appropriate path for a hopelessly retarded and ignorant transportation engineering culture like the only in which we’re stewing.

      I don’t have this all at my fingertips now, but I’ve had more than adequate success in the past, for all the good that has done.

  5. Charles Smith

    I greatly enjoyed this esay and admire the overall body of work. A couple of minor points –

    1. You suggest two platform tracks per tunnel track. Let me translate this to concrete terms that I understand. If one is using matched sets of tunnel tracks one pair going in each direction, then 2 North River tracks, paired with 2 East River track, for a total of four tunnel tracks need 8 platform tracks to deal with the potential traffic volume. With modern signalling and automatic train control, a max tunnel speed of 60 mph and consistent acceleration and deceleration of trains going through the tunnel, 1 min 30 sec headway between trains in the tunnel is possible; 1 min 30 sec headway means under ideal conditions 40 trains per hour going through the tunnel on one track in a given direction. Given two tunnels, 40 trains per hour in each direction is possible. With four platform tracks in each direction, that’s 10 trains per hour headway if optimally scheduled, or a new train every 6 minutes. Maintaining at least a one minute headway between trains at the platform, this leaves less than five minutes to empty and reload,
    not impossible. This will be facilitated by taking two steps:
    a. ensuring more than sufficient direct connections about 800 feet apart between every platform and the IRT and the IND.
    b. dramatically improving the flow off the platforms into the station and thence to the street. Tripling and quadrupling the escalators is necessary; widening the platforms will facilitate this step. Moving the NJ Transit offices from the mezzanine and using the volume to facilitate platform access will also help. The mid-platform access bridge that is part of the Moynihan station project should be implemented long before the rest of the project because it will help so significantly.

    2. A useful rule of thumb is to estimate minimum headway for trains on a track by adding one minute to the emergency stopping time for a train, assuming emergency deceleration of 0.1g or approx 1mph per sec. Thus, the faster the train, the greater the required temporal headway between train. A 120mph (approx 200kph) train needs approx 2 minutes of headway. A 240mph (approx 400 kph) train needs approx 3 minutes of headway. So, on the same track, the faster the train, the fewer the number of trains that can safely be operated – 40 trains per hour at 60mph, 30 trains per hour at 120mph, 20 trains per hour at 240mph. (In this last case, I might argue for a higher emergency deceleration rate, and thus increase train density, but it doesn’t counter the basic argument.)

    • Adirondacker12800

      40 trains per hour at 60mph

      Nobody in the world does that. Not at 60 MPH/100KPH. 80 trains an hour the only thing that could be in the station would be platforms and egress. A great many of people walk to their destinations because it’s almost as fast to walk as it is to take the subway. They were predicting 48 to 52 trains an hour when ARC and the current station reached capacity sometime after 2030. And pedestrian traffic jams as far north as 37th Street. as it is now people walk in the street instead on the sidewalk during peak.

      If there are 80 1,000 passenger trains an hour going past it’s worth it to consider sending some of them someplace else. Wall Street and Brooklyn. Rockefeller Center…

      • Eric

        If the sidewalks are too crowded for all the pedestrians, the solution is to take a couple lanes of traffic for pedestrian use, not to spend billions on a brand new terminal elsewhere (with no connectivity to the old terminal).

        • Adirondacker12800

          But not building anything isn’t one of the choices.. The choice is spending billions or spending billions. Spending billions to relieve overcrowding by giving people alternatives… gives people alternatives. And will speed up their trips. To keep the math simple if there are 60 trains an hour coming into Manhattan from Long Island and 60 an hour leaving for New Jersey and ten branches on each side that 6 trains an hour along each branch. Divert a third of them to Wall Street and that’s 40 an hour to Penn Station and 20 an hour to Wall Street. Instead of 6 trains an hour to Penn Station they have 4 trains an hour to Penn Station and 2 trains an hour to Wall Street. With just a bit of scheduling legerdemain they have 6 an hour to both with a cross platform transfer. They aren’t on the subway any more relieving overcrowding on the subway ( either NYC or PATH, PATH is at capacity ) The ones going to Wall Street get faster rides and everyone gets more pleasant rides.

          • Eric

            A regional rail connection to Wall Street would be a good thing, but very expensive. With one sub-Hudson tunnel you could drastically improve regional and intercity rail access to everywhere except Lower Manhattan and Brooklyn. It would take two underwater tunnels, plus lots of urban tunneling, to connect rail to Lower Manhattan. It is worth it someday, when many more billions are available, but right now there are higher priorities.

          • Charles Smith

            1. Adirondacker, you’re telegraphing the obvious next step, in your last comment, obviously you want to spread the passenger debarkations among stations. I am not so sure that you always want to spread the debarkations among trains. I am in the middle of a longer note that will come forward within the next couple of weeks, examining this a bit more extensively using Manhattan as an example.

            2. In response to the earlier comment that no one wants 80 trains each carrying a thousand passengers to come in and unload in an hour, I agree that the existence of demand in that magnitude is a significant problem. And, solving it is critical to the life of NYC.

            Today, 57 peak hour trains deposit about 62,000 passengers in Penn Station every workday. Fixing NJ transit will increase these numbers to about 80 trains depositing 80,000 passengers in Penn Station and carrying another 20,000 on to Grand Central.

            Where do today’s passengers come from? The LIRR currently brings 33 trains and approximately 40,000 passengers peak hour through the East River Tunnels into Penn Station NY, and terminates there. In 2019 (2029?) when “East Side Access” is complete and operating, LIRR projects bringing in 36 trains, but only 20,000 passengers to Penn Station NY peak hour.

            From the west side, NJ Transit currently brings 21 trains and 20,000 passengers through the North River Tunnels to Penn Station NY peak hour. NJ Transit’s own analysis of what it would like to bring in peak hour treating Penn Station as a terminal would appear to be ARC Alternative alt P, 50 trains and 38,000 passengers. You can’t get there from here with only 2 tracks under the North River.

            HOWEVER, by running through to either Long Island or Metro North, and putting in fully modern signalling and control, you can get to 34 trains per hour and more than 30,000 passengers from NJ (probably more if they ever build the parking they should), and still have 4 slots per peak hour left for Amtrak. Not bad for NO NEW TUNNELS in the short term.

            If one wants to think about putting in 2 tracks from Penn to Grand Central, but no new North River tunnel, and no run end-to-end interlining, one is looking at ARC alternative G. Alt G projects 34 NJ Transit trains inbound peak hour 20 of which go on to Grand Central. These trains bear 37,759 passengers under the North River (I wish I could forecast to 5 significant figures.), 24,344 of whom disembark at Penn Station while 13,415 continue to Grand Central Terminal. You also pick up 2,597 Metro North passengers who change at Grand Central and end their journey at Penn Station, for a total of 26,937 NJ Transit-related passengers exiting peak hour at Penn Station. All of this from adding two tracks from Penn to Grand Central.

            If one were to interline and offer a single seat service, the number of Metro North passengers continuing to Penn would likely double or more. If one were to interline so that 34 NJ Transit trains continue to and through Grand Central, there would also be increases in the number of passengers under the North River.

            If one were to go ahead and put in two new high speed tracks under the North River for a total of 4, and a total of four tracks from Penn to Grand Central, then one could comfortably provide the 52 trains in each direction necessary to link all Metro North and NJ transit services end-to-end, then one would be projecting 49,800 passengers or more peak hour passengers under the North River, 30,700 of which would disembark at Penn Station NY, while 19,100 would continue to Grand Central. (No estimate of North River traffic continuing north of Grand Central, sorry.) And, there would likely be at least 6,000 Metro North passengers continuing through Grand Central to Penn Station NY. This leads to a total of 36,700 NJ Transit-related passengers exiting trains peak hour at Penn Station NY.

            Thus running through to Grand Central has the quantitative benefit of offloading nearly 20,000 peak hour peak hour passengers from already crowded Penn Station to a facility with some spare peak hour capacity, while attracting at least 10,000 passengers to the rails from private cars and buses, who would otherwise be clogging the highways.

            Please note: I assumed no improvements on the LIRR side; these could make the projected demand noticeably worse. Also, please note, that the volumes of passengers departing Penn Station during morning peak hour has been ignored. If full reverse commute has its normal effects, these numbers will grow dramatically too.
            Please note further; this analysis ignores many improvements that are economically sound and would dramatically increase passenger traffic through Penn Station.

            All of the numbers but the 4 tracks through to Grand Central case are current official statistics or projections from Access from the Region’s Core Major Investment Study Summary Report 2003. The last numbers are my own back-of-the-envelope extrapolations from available data. As a statistician, I really do believe they’re a bit better than “rectal analysis”.

            3. Before saying, no one does this or has done this, think about the remarkable performance of the Pennsylvania Railroad in 1944 and 1945 particularly during November and December 1944. They manually moved extraordinary numbers of trains per hour in each direction through the North River tunnels on a sustained basis for hour upon hour, day after day.

            With this kind of density and uniformity of equipment, the problem we are describing is moving from that of standard railways, even with PTC, closer to that of heavy rail systems. The RER comes close. The Belgians do amazing things. Densities out of Shinjuku look like this. The level of sensor and electronic reliability required for a more complex task in a hostile environment was demonstrated and proved in practice with the Cat3B landing system for the L1011, which entered service more than 40 years ago, and has worked with 100% reliability ever since. (The principal engineering problems in attaining electronic reliability on that system were all issues of mechanical engineering.)

            4. My apologies for the length of the comment, but quantifying the problem is necessary for a rational discussion here.

          • Adirondacker12800

            The RER comes close.

            The RER isn’t a commuter railroad with ten branches all funneling down to four tracks. The usual number I see for RER line A is 30 per hour. If you want the trains to toddle along at 20 MPH between Jamaica and Manhattan or between Secaucus and Manhattan you might be able to squeeze in 30 an hour per. If you want the trains to pass through Woodside or Secausus at 60 MPH maybe not and you’ll have to settle for 25 an hour.

          • Alon Levy

            The RER A goes at 80-90 km/h through the central segment, depending on the station pair.

            And the Chuo Rapid Line, with its 28 tph turning at one two-track terminal, tops at 95 km/h.

            40 tph on mainline rail doesn’t exist, but 32 does.

          • Adirondacker12800

            and the speed limit on Portal Bridge used to be 90. Foamer videos claim that trains go through Secaucus at 90. The 12 minute train to Newark had to go more than 100 out in the Meadows to do that.
            The track maps that-are-no-longer-online say that the LIRR Main line’s speed limit is 80 between where the Port Washington Branch, branches and just west of Jamaica. So they are clipping through Kew Gardens at 80-ish. 26 trains an hour when there 80 and 90 mph railroad a few miles away, is very respectable. And if you try to shove 7 pounds of trains into that 5 pound bag you may end up with slower trains.

    • Charles Smith

      Switches a. tend to slow things down, both by limiting the speed of the train going over them, and by taking time to set and reset, even with powered remote control. Switches also take a lot of maintenance. The simplest way to avoid delays due to switching is to simplify the paths through the ladder.

  6. Charles Smith

    Yes, in 1938, the Santa Fe cleared the track completely an hour ahead of the Super Chief’s coming through. Hopefully, there’s been a bit of progress since then.

    From a control systems point of view, dealing with tunnel flow is not the same thing as controlling the whole commuter railroad. Tunnel flow from NJ depending on direction is not Zoo Interlocking. It has two sources and one sink going into Penn Station NY – Harrison and Secaucus on one end and the Penn Station track ladder on the other end. Effectively you have two queues merging into one going into the tunnel and one queue feeding out on the other end. Managing the flow through the track ladder so as to minimize delay is a second and separate problem, which Dr. Levy’s thoughtful essay is directed at solving. Note that the most effective solution is architectural. Beyond receiving trains into control queues going in and setting their priorities, the rest of the operation of the commuter railroad is largely outside the tunnel control issue.

    The sensor, signalling, and vehicle control issues for trains with tight headways at 60 mph or worse 400 kph are pretty well understood, and the technology is largely in hand. It can not be done just manually, although in the tunnel case it might be possible in extremis. Manually over-ridden, automatic Fail-SOFT control is inherent in PTC, particularly the moving block variant, and critical to achieving economical density on high speed lines. Putting the necessarily redundant sensors and communications in place is a pretty well defined task. And, the return in this carefully controlled case more than justifies the investment. How many billion would otherwise have to be spent to increase NJ Transit’s capacity into NYC by 13 trains at peak hour?

    The interesting thing about the economics of railway engineering is that often there are increasing returns to scale, especially with speed and density. At 100 kph, you’re lucky to cover marginal fuel and labor costs. At 200 kph, you cover operating expenses. At 300 kph, you cover all of the above plus depreciation. At 400 kph, you finally get to the point that you cover the capital investment as well. All of this is true even though the capital investment for 400 kph is 10 times the capital investment for 200 kph. We are so used to not having a truly financially sound proposition and/or not having access to the needed capital, that we often fail to think like the aircraft designer or communications system architect who starts with the needed performance and moves backwards to the architecture and implementing technology.

    In the case of HSR from the Atlantic as far as the west bank of the Missouri River, in Texas, and west of the Sierra’s, the financial case is compelling. In the case of building appropriate transport for the New York City area, the economic and particularly the socio-economic cases are compelling and, I believe, a winning financial approach can be developed, BUT ONLY if we step out of the box a bit every step of the way.

    I served in submarines. There is no more conservative/high risk engineering environment; yet pushing the technology envelope there had increasing returns to scale as well.

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