Fix the Slowest Speed Zones

I am wrapping up a project to look at speedup possibilities for trains between New York and New Haven; I’ll post a full account soon, but the headline result is that express trains can get between Grand Central and New Haven in a little more than an hour on legacy track. In this calculation I looked at speed zones imposed by the curves on the line. The biggest possible speedups involve speed limits that are not geometric – and those in turn come from some very sharp slow zones. The worst is the Grand Central station throat, and I want to discuss that in particular since fixing the slowest zones usually yields the most benefits for train travel times.

Best practice for terminal approaches

Following Richard Mlynarik’s attempt to rescue the Downtown Extension in San Francisco, I’ve assumed that trains can approach terminals at 70 km/h, based on German standards. At this speed, an EMU on level track can stop in about 150 meters. In Paris, the excellent Carto Metro site details speed limits, and at most terminals with bumper tracks the speed limit is 60 km/h, with a few going up to 100 km/h.

Even with bumper tracks, 70 km/h can be supported, provided the train is not intended to stop right at the bumpers. At a fixed speed, the deceleration distance is the inverse of the deceleration rate. There is some variation in braking performance, but it’s in a fairly narrow range; on subway trains in New York, everything is supposed to brake at the same nominal rate of 3 mph/s, or 1.3 m/s^2, and when trains brake more slowly it’s because of a deliberate decision to avoid wearing the brakes out. As long as the train stops 1-2 car lengths away from the bumpers, as is routine on Metro-North, the variation will be much smaller than the margin of safety.

Fast movement through the station throat is critical for several reasons. First, as I’ll explain below, sharp speed limits have an outsize effect on trip times, and can be fixed without expensive curve easements or top-rate rolling stock. And second, at train stations with a limited number of tracks, the station throat is the real limiting factor to capacity, since trains would be moving in and out frequently, and if they move too slowly, they’ll conflict. With its 60 km/h throat, Saint-Lazare on the RER E turns 16 trains per hour at the peak on only four tracks.

American practice

I had a conversation with other members of TransitMatters in Boston yesterday, in which we discussed work to be done for our regional rail project. One of the other members, I forget who, asked me, do European train protection systems shut down in station throats too?

The answer to the question is so obviously yes that I wanted to understand why anyone would ask it. Apparently, the American mandate for automatic train protection on all passenger rail lines, under the name positive train control, or PTC, is only at speeds higher than 10 miles per hour. At 10 mph or less train operators can drive the train by sight, and no signaling is required, which is why occasionally trains overrun the bumpers even on PTC-equipped lines if the driver has sleep apnea.

Without video, nobody could see the facial expressions I was making. I believe my exact words were “…What? No! What? What the hell?”.

The conversation was about South Station, but the same situation occurs at Grand Central. Right-of-way geometry is good for decent station approach speed – there is practically no limit at Grand Central except tunnel clearances, which should be good for 100 km/h, and at South Station the sharp curve into the station from the west is still good for around 70 km/h given enough superelevation.

The impact of slow zones near stations

Last year, I published code for figuring out acceleration penalties based on prescribed train characteristics. The relevant parameters for Metro-North’s M8 is initial acceleration = 0.9 m/s^2, power/weight = 12 kW/t. Both of these figures are about two-thirds as high as what modern European EMUs are capable of, but it turns out that at low speed it does not matter too much.

Right now the Grand Central throat has a 10 mph speed limit starting just north of 59th Street, just south of milepoint 1. The total travel time over this stretch is 6 minutes, a familiar slog to every regular Metro-North rider; overall, the schedule between Grand Central and Harlem-125th Street is 10 minutes northbound and 12-13 minutes southbound, the difference coming from schedule padding. The remaining 65 or so blocks are taken at 60 mph, nearly 100 km/h, and take around 4 minutes.

Now, let’s eliminate the slow zone. Let trains keep cruising at 100 km/h until they hit the closer-in parts of the throat, say the last kilometer, where the interlocking grows in complexity and upgrading the switches may be difficult; in the last kilometer, let trains run at 70 km/h. The total travel time in the last mile now shrinks to a minute, and the total travel time between Grand Central and Harlem shrinks to 5 minutes and change. Passengers have gained 5 minutes based on literally the last mile.

For the same reason, the Baltimore and Potomac Tunnel imposes a serious speed limit – currently 30 mph through the tunnel, lasting about 2 miles; removing this limit would cut 2-2.5 minutes from the trip time, less than Grand Central’s 5 because the speed limit isn’t as wretched.

The total travel time between New York and New Haven on Metro-North today is about 1:50 off-peak, on trains making all stops north of Stamford. My proposed schedule has trains making the same stops plus New Rochelle doing the trip in 1:23. Out of the 27-28 minutes saved, 5 come from the Grand Central throat, the others coming from higher speed limits on the rest of the route as well as reduced schedule padding; lifting the blanket 75 mph speed limit in Connecticut is only worth about 3 minutes on a train making all stops north of Stamford, and even on an express train it’s only worth about 6 minutes over a 73 kilometer stretch.

What matters for high-speed travel

High-speed rail programs like to boast about their top speeds. But in reality, the difference between a vanilla 300 km/h train and a top of the line 360 km/h only adds up to a minute every 30 kilometers, exclusive of acceleration time. Increasing top speed is still worth it on lines with long stretches of full-speed travel, such as the Tohoku Shinkansen, where there are plans to run trains at 360 over hundreds of kilometers once the connection to Hokkaido reaches Sapporo. However, ultimately, all this extra spending on electricity and noise abatement only yields a second-order improvement to trip times.

In contrast, the slow segments offer tremendous opportunity if they are fixed. The 10 mph limit in the immediate Penn Station throat slows trains down by around 2 minutes, and those of Grand Central and South Station slow trains by more. A 130 km/h slog through suburbia where 200 km/h is possible costs a minute for every 6.2 km, which easily adds up to 5 minutes in a large city region like Tokyo. An individual switch that imposes an undue speed limit can meaningfully slow the schedule, which is why the HSR networks of the world invented high-speed turnouts.

Richard Mlynarik notes that in Germany, the fastest single end-to-end intercity rail line used to be Berlin-Hamburg, a legacy line limited to 230 km/h, where trains averaged about 190 km/h when Berlin Hauptbahnhof opened (they’ve since been slowed and now average 160). Trains go at full speed for the entire way between Berlin and Hamburg, whereas slow urban approaches reduce the average speed of nominally 300 km/h Frankfurt-Cologne to about 180, and numerous compromises reduce that of the nominally 300 km/h Berlin-Munich line to 160; even today, trains from Berlin to Hamburg are a hair faster than trains to Munich because the Berlin-Hamburg line’s speed is more consistent.

The same logic applies to all travel, and not just high-speed rail. The most important part of a regional railway to speed up is the slowest station throats, followed by slow urban approaches if they prove to be a problem. The most important part of a subway to speed up is individual slow zones at stations or sharp curves that are not properly superelevated. The most important part of a bus trip to speed up is the most congested city center segment.

29 comments

  1. Bruce

    Interesting article. GCT could add a lot of capacity and convenience if it was used more. Haven’t taken a train into there in quite a while but what you say doesn’t surprise me. To put it bluntly the problem is the rail cabal is giving us the finger. It’s always based on “exigencies” – reasons.The same will be the end of GCT if they get their way.

  2. seb

    I’m not so sure about the speed limits on the Carto Metro site as coming into Saint-Lazare, the trains are much slower than 60 km/h. On the Frankfurt-Cologne line, the problem on the Cologne side is that the dedicated high speed line begins only after 9,2km of shared track, but there are plans to separate them. Also, the trip over the Hohenzollernbrücke is just too slow.
    In general, it’s crazy to spend billions on a new high speed line to save a couple of minutes and then not invest in so many low hanging fruits.

    • Jhonny

      The mentioned bridge is one of Germany’s most congested rail lines. A sane government would have invested into expansion/replacement decades ago

  3. Diego Beghin

    Sometimes there’s a trade-off between speed and capacity, right? In Brussels, the North-South junction is the lynchpin of the national railway system, 1/3 of all trains go through it. The speed limit is only 50 km/h, probably because a slow and steady stream of trains is better than hitting too many red lights.

    • Jhonny

      The trade-off is not as much speed and capacity as moving slow and fast trains.

      If you have slow trains and fast trains at the same time, capacity tanks. Even timed overtakes need a bit of schedule padding…

  4. ckrueger99

    Another advantage of the thru running of an S-Bahn-type layout is that the approaches to the would-be terminal no longer have a complex throat layout, so the go-slow zone near the station is much smaller. Compare Philly before and after the Center City Connector was built in the ’80s: Before, both Suburban and Reading Terminals had complex throats leading to around 12 terminal tracks. Today, with only 4 complete through running tracks, the lines merge at higher speeds further out (North Philadelphia or Zoo, for example) and trains can approach 30th or Jefferson (Market East) at higher speeds. I’m sure SEPTA could improve this, also, especially after the Silverliner IVs are retired in coming years.

    • Jhonny

      This is just pro Stuttgart 21 propaganda!!!!

      OBVIOUSLY terminus stations are superior to through stations in every way!!!!!

  5. Jacob Manaker

    You say that your Boston colleague asked if European ATC shuts down in station throats. Did you mean stays active?

    (I tried to figure it out from the link to the Int’l. Railway Journal [text “obviously yes”], but that links seems broken.)

    • Alon Levy

      The link is not broken, the site just doesn’t load the text. Hit Ctrl+U to see the source and you’ll see the article.

      And yes, ATP here stays active in station throats.

    • F-Line to Dudley

      Jacob…the cab signals stay active all the way to the bumper post. At sub-10 MPH the engineer has ability to manually override them in case of a signal dropout, since that’s a relatively common glitch when going through the gut of a maze of yard or terminal switches. The train will get blown for a stop penalty if it exceeds 10 MPH, but manual override is possible from 0-10 MPH provided the engineer takes direct action to override every signal readout.

      In theory bumper post accidents at stub-end terminals like Hoboken are supposed to be preventable by the ever-increasing number of signal readouts as the tracks divide at switches into the platforms, and the slow zone shouldn’t need to be excessively long because of that. But in the case of Hoboken an engineer who conditioned his hand movements at the throttle to cheat over time was able to “sleepwalk” through. The regressive approach is to keep chucking restricting codes further and further out so there’s more warnings and less chance of splitting a switch en route to the platform. Cab signals have been around on the Northeast Corridor since the first test installation in 1922, and through much of present-day MNRR, LIRR, NJT, SEPTA, and MARC since prewar times. That’s 95 years worth of regressive patching until you end up with terminal approaches excruciatingly slow across the board, and such excessive warning that lazy employees can counterintuitively game the system.

      It’s not so much that the adopted tech is bad as that the decades of accumulated Signal Dept. cruft has gunked up the throats of these major terminals beyond recognition. A clean do-over of the cab signal layout in any of these throats should be able to fix those efficiency issues. While a correct programming of the new PTC overlay installations should be able to utilize PTC’s ability to positively enforce stops (instead of just penalty-enforcing like the cabs) and close the loopholes around running aground at a bumper or splitting a switch in a tunnel. Especially since PTC is a wireless pickup and doesn’t have the same risk of momentary signal dropouts like the running rail- transmitted cab signals do when a train is passing through a heavy thicket of switches; PTC wouldn’t need to wield speed restrictions like a blunt instrument around the dropout issue.

      Redoing the signal layout is a considerable undertaking, which is why RR’s were reluctant to do so all these years with their cab signals. But now that the PTC deadline is forcing them to do a lot of backbreaking signal work hell or high water a lot of trash is getting taken out. We’ll see in another year or so when these terminal installations are live and debugged if the results are anything like they could be.

  6. rational plan

    In the UK whenever a stretches of track are due for resignalling, a very expensive process. It is standard for other rail improvements to be planned. Typically being new junctions layouts, track realignments plus new sections of track, to increase capacity and improve line speeds through station areas. It is at this time extra platforms are often built.

    The Great Western Modernisation of the line from London to South Wales is finally coming into it’s closing stages. And is line first major investment since the 1980’s. A smaller scale can be seen in the Derby Station blockade where they’ve added more platforms and remodelled several miles of track and junctions. Changing station approaches from 20mph to 40 mph makes a big difference, more common is allowing the mainlines to run at full speed through smaller stations.

  7. F-Line to Dudley

    Alon…it’s cab signals that allow the sub- 10 MPH engineer override. The PRR pulse-code cab signals prevalent through the Northeast U.S. have always had the 10 MPH cutout for coexisting inside yard limits with switching activity, as high-activity yard limits are a major source of signal dropouts. Since the ACSES PTC system adopted by all NEC-member passenger railroads is built as an overlay to the existing cab signals and permits continued full-speed operation should one system fail, the legacy speed for engineer override is retained in the legal mandate. That’s not nearly as relevant to railroads in the rest of the country where PTC is being applied to lines that never had cabs/ASC to begin with, and is reflected as such in the comprehensive PTC plans each road had to submit for FRA approval.

    That does NOT mean that the PTC is crippled-by-fiat at low speeds. PTC can be programmed to do whatever you want it to, including new things like getting instant bulletin readouts for hour-by-hour slow zones for the presence of track workers in a given area (which should greatly reduce RR employee accidents & fatalities). Plugging the slow-speed engineer error loophole that allowed for the Hoboken Terminal disaster of a couple years ago is doable with PTC. It actually was possible with just the cab signals by properly auditing the signal layout in the Hoboken Terminal district for loopholes and adding extra speed enforcement warnings, just as Metro-North and Amtrak got the book thrown at them by the NTSB for gaps in ASC enforcement in the Spuyten Duybil and Frankford Jct. disasters. PTC just makes that hole-plugging much easier to implement and fine-tune.

    Of course, you have to progressively treat the signal layout if you want to fortify the areas of maximum risk at a GCT or Hoboken from operator error while simultaneously optimizing the dog-slow approaches for a little more zip by shortening up the areas of too-much-excess caution. Regressively sticking another individual restriction on top of 50 years of accumulated restrictions without looking at the whole living/breathing animal of course just ends up making things worse. But that’s a management problem, not a technological problem. A perceptive Signal Dept. with full backing from upper mgt. can do optimization right using the tools at hand.

  8. adirondacker12800

    The total travel time in the last mile now shrinks to a minute, and the total travel time between Grand Central and Harlem shrinks to 5 minutes and change.

    After you seen the accurate three dimensional drawing of everything south of the tunnel portal. 3-D – two levels, ramps, columns holding up skyscrapers etc. would make it bit complex.

    lifting the blanket 75 mph speed limit in Connecticut is only worth about 3 minutes on a train making all stops north of Stamford, and even on an express train it’s only worth about 6 minutes over a 73 kilometer stretch.

    Which is probably why Connecticut doesn’t spend the money to maintain the track for Class 5/90MPH and settles for Class4/80MPH. Class 6 or 7 would be too aspirational. … wouldn’t “north of Stamford” be the New Canaan branch?

    the Baltimore and Potomac Tunnel imposes a serious speed limit – currently 30 mph through the tunnel, lasting about 2 miles; removing this limit would cut 2-2.5 minutes from the trip time, less than Grand Central’s 5 because the speed limit isn’t as wretched.

    Assuming the clearance is there, they did a lot of finagling to get catenary into it. That tunnel should be put out of our misery before it drops a chunk of ceiling on a train. Or something more spectacular like collapsing for a few blocks. If I remember correctly the new tunnel saves a much more. Lots of it by arriving or departing Penn Station Baltimore at higher speed and hitting fresh air in West Baltimore at 125.

    The most important part of a regional railway to speed up is the slowest station throats, followed by slow urban approaches if they prove to be a problem.

    In North America, once they have level boarding at the suburban stations. Level boarding is relatively quick and cheap. There may be problems at some stations. One of the rumors floating around is that they made the platforms in Hoboken part of the historic building and that means no level boarding in Hoboken. The sheds over the platforms are too low. Some suburban stations won’t get level boarding until someone finds funding to jack up the historic landmark station building too. And regrade everything around it in sensitive manner… There are some special cases. ARC and I would hope Gateway, in normal service, saved ten minutes between Broad Street Newark and Manhattan by separating Morris and Essex traffic from Northeast Corridor traffic. Separating both of them from each other saves another few. Which saves the same amount of time on an Amtrak train.

    • Max Wyss

      How difficult would it be to lower the tracks in Hoboken? Or are the tracks also part of the historic building?

      • adirondacker12800

        Hoboken is right at the waterfront, some of the tracks flood during exceptionally high tides. There are PATH tracks under it. I’d hazard a guess it would be difficult. The long term solution is to carry the suburbanites directly to downtown Manhattan so they aren’t clogging PATH. Something clever like running through to Jamaica so Long Islanders can avoid going through Midtown, would be good. “Wall Street” is the country’s third or fourth largest central business district, two tracks of suburban railroad would be well used.

        • Max Wyss

          Absolutely, through-running to Manhattan (and continuging beyond) would be the solution of choice.

    • Alon Levy

      Removing the B&P limit obviously means building a new tunnel, the existing one has real ROW geometry constraints, even if they’re not quite as bad as 30 mph. And the 2 minute figure is taken from last decade’s FRA study about the B&P replacement, the one recommending the Great Circle Tunnel alignment saying it would cost $750 million.

      And there are a lot of straight paths to the platform tracks at Grand Central. It’s not just slow switches in the interlocking. Ditto Penn Station – the speed limit on the straight paths is the same 10 mph.

    • The Economist

      We are way too stuck on historical significance when it comes to places like Hoboken. What exactly is historic in the platforms in Hoboken? The crumbling concrete that is a tripping hazard? In Europe, they would have raised up the canopies over the platforms by cutting the columns and inserting extra steel at the bottom and pouring new concrete platforms. Yes, it would not be the original look, but it would be a look that preserves 90% of the original stuff for generations to come. Here we let the historical station decay until it becomes a safety hazard and then it will be razed altogether. The same will eventually happen at Newark Penn. The platforms there are decaying at a similar rate.

      • adirondacker12800

        Amtrak sold Penn Station Newark to NJTransit. NJTransit spent a lot of money on it. The parts of the platforms that could serve 16 car trains might be a bit decrepit but Penn Station Newark is in pretty good shape. It’s also landmarked.
        Raising shed roof costs money. Or tearing it down and replicating it, that is an option for historical buildings. One of the options could be to abandon Hoboken and send the suburbanites directly to Wall Street. They wouldn’t be on PATH, which is overcrowded. ….straighten the sharp curve west of Hoboken and they might even be able to squeeze another train or two an hour through the system.

  9. Max Wyss

    As there are a few references to Switzerland…
    The current signalling system uses “switching paths” (Rangierfahrstrassen), which are governed by dwarf signals. Before a main road path can be established, the switching path has to be set and locked. Only when this is set, the main line signals open.
    Switching occurs on view; the dwarf signals have three aspects: proceed, proceed to the next dwarf (which shows stop), and stop. There is no further control, although the control center would be alerted if a movement passes beyond a dwarf showing stop.
    Any switching move has a speed limit of 40 km/h, which is also the speed “standard” switches can be passed on deviation.
    In a stub end terminal, such as Zürich HB, tracks 3 to 18, operation after the home signal is in switching mode, in other words on view (however, when the home signal is open, the switching path to the bumper of the target track is set). There is a speed supervision at the home signal, which is the switching speed of 40 km/h. This is also the speed limit when departing, until the main signal is passed. If I remember correctly, there are a few paths (terminal track to mainline) where the 40 km/h limit ends earlier (because there are no switches on deviation in that path during most of the yard area).

    I am shocked to read that the US switching speed is 10 mph. So, speeding up the station throats to the Swiss speed of 40 km/h would shorten the time considerably. There is an old rule in motion mechanics: keep the slow movements as short as possible; that’s where you control the cycle time (some years ago, I had a customer who made the devices to move glass bottles coming on a rast conveyor belt from the glass blowing machine onto the slow conveyor belt of the cooling oven; there the time available for a cycle was given by the speed of the incoming belt and the width of the cooling oven. a few milliseconds more, and bottles ended up on the floor; that teaches you to be careful with slow speeds).

    The question of supervision switching movements becomes eminent if one would do full supervision until the end of a stub end track. ETCS L2 does have the means to do so, but it is getting very complicated, the more complex the station throat is. The link in the article to the Swiss Traffic Management system leads to a report about “smartrail 4.0”, a project involving some Swiss railroads, the industry, and the supervising organs, which is intended to use IT to increase capacity and safety. One of the key topics is the assured knowledge of the train’s exact position (looks like a key function of PTC as well, although GPS is not good enough for that purpose). When this is solved, switching movements can also done under full supervision (and may eventually lead to automatic switching). (note, the smartrail 4.0 website is at the moment plastered with buzzwords, but the download section has quite a few interesting documents).

  10. Max Wyss

    Turning around 16 tph on a 4-track terminal is quite good, that gives an average of 4 trains per hour per track. There are only very few places where they do more; Bern RBS comes to my mind where the 4 terminal tracks do 20 tph at peak, and 2 specific tracks in München Ostbahnhof, where they turn around 6 trains per hour per track (although the paths to and from those tracks do not vary).

    • Alon Levy

      Yeah, it’s definitely not typical. In the same conversation people asked me for limiting values of turnaround times, and I explained that usually these are at terminal stations where intercity trains change direction, like Frankfurt on some ICE lines (or Philadelphia on Keystones in the US), because for the most part the big city terminal stations have a ton of tracks. The big-city S-Bahns all have through-running infrastructure by now, even when mainline trains don’t, like in Frankfurt and Stuttgart, so there’s no place where there would even be an opportunity for fast turnarounds. But where it’s needed, like when they built the RER E tunnel, they do it.

      • Max Wyss

        Actually, during one of my (not so frequent) trips between New York and Harrisburg, I encountered very quick turning around in Philadelphia. However, I don’t know if the driver changed, and the departing driver was waiting at the spot; changing driver when changing direction can save another 2 to 3 minutes, as soon as the control from the incoming cab is deactivated, it can be established from the outgoing cab.

        • Jhonny

          I saw a documentary about “a day in the ICE” once and there it was standard that the outgoing driver told the incoming one about Abby issues that were encountered on the trip so far and any defects encountered

  11. Oreg

    You raise an interesting point about breaking on the NYC Subway: Why do they still not have regenerative brakes, more than a century after those were invented?

      • Oreg

        Ah, that’s good to hear. Thanks much for the reply.
        In fact, that could even help somewhat with the heat in the stations as traditional breaks convert all the kinetic energy of the train into heat against only a fraction for regenerative breaks.

        • Trainluvr

          My understanding of NYCT regenerative braking (not breaks) is that power may only be fed back into the third rail if there is another train in that section taking up power. If not, then the juice generated from a braking train’s motors must be dissipated as heat.

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