MBTA-HSR Compatibility

There is going to be major investment in the Northeast Corridor, and several possibilities, including Amtrak’s NEC Master Plan, call for running trains at higher frequency and somewhat higher speeds than today on the Providence Line, and assumes electrification of commuter service. Since the line is already being used by the MBTA, which according to Amtrak is limiting the number of intercity train slots for capacity reasons, this calls for a good measure of schedule integration, based on the principle of organization before electronics before concrete.

Amtrak’s Master Plan calls for three-tracking the entire Providence Line south to Attleboro (one viaduct excepted) instead, at a cost of $464 million – $80 million in Phase 1, $384 million in Phase 2 – in addition to money spent on unnecessary expansion at South Station. Such a cost is excessive, suggesting that better MBTA-HSR compatibility is required. Full-fat HSR programs go even further and avoid the Providence Line in favor of a greenfield alignment or an I-90 alignment, instead of making use of the existing high-speed track in Rhode Island and Massachusetts. To reduce costs, a better plan would four-track short segments for passing sidings, and time the overtakes. The principle is similar to that of the blended Peninsula plan in California, in the version proposed by Clem Tillier.

In many ways, for example the metro area populations involved and the current ridership level, the Providence Line is similar to the Caltrain line. The main difference is that the Providence Line has fewer stops and therefore can expect higher average speeds. In addition, the Providence Line is straighter and passes through less developed areas, so that even today Acela trains plow it at 240 km/h, and about 330 km/h is possible with true high-speed trains and higher superelevation.

In Switzerland, trains run as fast as necessary, not as fast as possible. In this context, this means running just fast enough to meet a good clockface schedule. Boston-Providence travel time on the MBTA today is about 1:10; for a good takt, this should be cut to about 55 minutes, allowing hourly service with two trainsets and half-hourly service with four.

For the purposes of schedule symmetry and avoiding switching moves at high speed, passing segments should have four tracks rather than three when possible. Costs should be controlled by making those passing segments much shorter than the three-tracking Amtrak proposes.

Finally, the timetables proposed here are based on the following performance assumptions: regional trains have a top speed of 160 km/h, accelerate like a FLIRT (45 seconds acceleration plus deceleration penalty), have an equivalent cant of 300 mm, and dwell at stations for 30 seconds. Intercity trains accelerate like an idealized N700-I, have an equivalent cant of 375 mm, and dwell for 60 seconds. The equivalent cant is by and large unimportant; the acceleration and dwell times for regional trains are. The approach into and out of South Station has a speed limit of 70 km/h through the 90-degree curve toward Back Bay, and 100 km/h to south of the curve at Back Bay; intercity trains are limited to 200 km/h south to Readville and 250 km/h south to the Canton viaduct, and, at the southern end, 225 km/h west of the curve in Attleboro and, curves permitting, 200 km/h in Rhode Island. Regional trains turn in 5 minutes, or 4 at a minimum, and intercity trains turn in 10 minutes at a minimum. Signaling allows a headway of 2 minutes at a speed of 200 km/h and 3 minutes at higher speed, but if a regional train starts from a siding stop, it can follow a high-speed train more tightly initially, say 1 minute, still far higher than a safe stopping distance, since the spacing rapidly increases over time. Grades are ignored; the Providence Line is flat enough that they’re not an issue. Timetables should be padded 7% from the technical time.

With the above assumptions, the technical time for regional trains is 38 minutes with the present stopping pattern, which yields 41 minutes with padding; this compares with 46 minutes for the fastest Acela. Clearly, if Acela service levels remain similar to what they are today – which includes the Master Plan, which calls for a 10% reduction in Boston-New York travel time (see page 40 on the PDF linked above) – there’s no need for passing segments. To raise travel time to 55 minutes, trains should make more frequent stops, and/or run to T. F. Green Airport always. Although the speed profile of regional and intercity trains would be different, the average speed would be the same, and given that the corridor has a small number of trains per hour of each type, this mismatch is no cause for concern. The $464 million Amtrak is proposing would then be a complete waste, and the federal government should spend any money toward this goal on electrifying more MBTA lines and funding EMUs.

However, in a scenario involving a significantly improved intercity service, the best technical time for nonstop Boston-Providence service with a top speed of 300 km/h decreases to about 19 minutes (20.5 with pad), and this makes overtakes necessary. A slowdown to 250 km/h only adds about one minute of travel time, so the operating pattern is almost identical.

If 15-minute service, both regional and high-speed, is desired, then regional trains can be about 11 minutes slower between successive passing segments, since 11 = 15-3-1 or 15-2-2. A single mid-line overtake is theoretically possible: 41-20.5 = 20.5 < 2*11. However, such an overtake would have to be exactly at the midline, and, in addition, there could be merge conflicts at Providence, whose station tracks include two on the mainline and two on one side of the mainline as opposed to one on each side.

It’s still possible, but tight, to have a single overtake at Sharon. The immediate station vicinity would be four-tracked; this is no trouble, since the area around the station is undeveloped and reasonably flat. In addition, there’s more than enough time in the Providence area, making the merge conflict a lesser problem. However, this is very tight near Boston South, beyond signaling capability unless four-tracking extends a few kilometers further north. One way to counter this problem is to slow high-speed trains by making them all stop at Back Bay and/or Route 128, adding precious minutes to the schedule but reducing the speed difference. Conversely, the current weekday pattern of Providence Line trains skipping Ruggles could be made permanent. There is no room for infill stops; the overtake would only add 4 minutes to regional train travel time, so there’s time to run further to the airport at 160 km/h, and even make an extra stop at Cranston.

Another possibility is to have two overtakes, taking advantage of existing four-tracking around Attleboro. The capital costs are similar; it would require four-tracking around Route 128, possibly extending north to Readville if an on-the-fly overtake is desired. The operating complexity is much higher, since there’s one more opportunity for a late train to mess up the entire schedule. However, there is plenty of slack south of Attleboro and north of Route 128 allowing for additional stops. Under this option, the train loses 4 minutes waiting at Attleboro and about 2.5 at Readville, since the overtake is not completely on-the-fly, raising travel time to 47.5 minutes. There’s no time for airport trains, not on the same takt. However, there’s space in the schedule for 5-6 infill stops in addition to Readville; Forest Hills, Pawtucket, Central Falls, and perhaps one more in each of Boston and Providence closer to city center.

In principle, it’s possible to extend this analysis to 10-minute service, with three overtake segments, at Route 128, Sharon, and Attleboro. In practice, this is operationally cumbersome, and the operating profits coming from filling six full-length high-speed trains from New York to Boston ought to be able to pay for four-tracking the entire line, even the viaduct.

Not included in this analysis are the branches. Those are not a worry since north of Readville there are three tracks, and frequencies on the other lines are low. The Stoughton Line is a bigger problem; however, with the three tracks through Boston, it could still be shoehorned. Electrifying it should not be difficult due to its short length, though the proposed Taunton extension would make it harder.

31 comments

  1. Alon Levy

    To clarify, the plan here does not obviate the need for additional concrete – at a minimum, level boarding at all stations, and maybe also grade-separating the junction between the Providence and Franklin-Fairmount Lines. However, level boarding at the 6 stations that have low platforms is more than an order of magnitude cheaper than three-tracking several tens of kilometers.

  2. ant6n

    Do you really expect 4tph+4tph on this line? Or even 6tph+6tph?
    It seems that it should be possible to construct schedules without any overtakes, assuming 20min service on the different lines. One could also, for example, integrate the fares of the North East regional with the MBTA to get more frequent express service between Boston and Providence, without having to run dedicated commuter trains.

    Another way is to make the MBTA trains faster. In Germany there’s a “regional express” Nurnberg-Munich (171km) running on a HSR line, which runs at a speed of 200km/h rather than 160km/h, in order to fit among the HSR lines (http://en.wikipedia.org/wiki/M%C3%BCnchen-N%C3%BCrnberg-Express) (…oh, and it seems to be loco-hauled)

    Combined with some of these ideas is the possibility to add more stations only along the first half (or so) of the line – and run that line only that long. Stopping patterns like this can make it possible to integrate a bunch of different trains on the same track:

    *******
    *——*–*—*-*-*-*-*
    *————-*——–*—-

    Integrating such different train types with 10-minute intervals and so many overtakes seems like a bad idea. I think in some German cities, there are S-Bahn and regional services (trains with similar speeds) that mingle together at these intervals, and the schedules are not very robust.

    To what extend do stations have to be modified, in order to allow trains passing at 300km/h?

    • Alon Levy

      6+6 is probably fantasy at this stage – and, as I said, if it’s required, then there’s going to be enough money for four-tracking. 4+4 is high, but 4 tph HSR is about in line with what we should expect from full-fat HSR in the Northeast, and 4 tph commuter rail is somewhat higher than current peak frequency. 3+3 is not enough to have a zero-overtake schedule – trains would have 16 minutes, which is too little – but should be enough to do just one overtake at Attleboro, if there are no additional stops to the north.

      Running trains at 200 km/h is mainly an option between Sharon and Attleboro, where the station spacing is very wide. It saves about a minute, if I’m not mistaken. Elsewhere, trains just wouldn’t have enough time to hit 200 km/h; the FLIRT takes 2 kilometers just to accelerate to 160 and about 1 to decelerate, and the stop spacing between Hyde Park and Sharon is 5.2 km, leaving very little room to run faster.

      One way to do what you propose with local and semi-express stations is to use Stoughton Line trains as the locals. In that case, a maximum of 4+4+4 can work, with locals departing South Station 2 minutes after express commuter trains and 4 minutes after intercity trains. It’s tight if the locals stop at both Forest Hills and Readville in addition to the usual Providence Line stops, and loose if they stop at just one or the intercity trains stop at Back Bay. The problem with such an arrangement is the express commuter trains still have to be overtaken somewhere, and they only get to skip two existing stops (Ruggles and Hyde Park); together with 200 km/h running this is enough to move the overtake point from Sharon to Mansfield, but not to Attleboro. Using Attleboro would require all intercity trains to stop at Back Bay and Route 128.

      I doubt station platforms have to be modified to allow high-speed passing. The stations are typically high-platform for one car length, providing accessibility but not level boarding, and are bypassed by the Acela at 240 km/h every day.

      • ant6n

        There’s other little games with schedules one can play. For example during the morning rush the number of commuter trains going Boston->Providence may not be at peak frequency yet, and may allow extra slots for express trains Boston->NYC.

        At the same time NYC->Boston express trains could start in New York, which would arrive at 10 or so – just in time to allow some of the commuter rail slots to be used by the express hsr trains.

        So one could create a rush-hour 4tph, otherwise 2tph ‘local’ train. Combine that with allowing local tickets on some of the faster trains to get more frequent service between Providence and Boston. And this means that during (morning) rush hour you get peak frequency on the destinations
        Providence->Boston,
        Boston->NYC,
        NYC->Boston.

        • anonymouse

          I think a good off-peak service level is 3 tph: one “HSR” to Washington, one “Regional” to NYC or DC making more stops south of Providence, and one local, which makes for no schedule conflicts at all. The AM peak is indeed fairly easy to deal with given that southbound commuter service is reverse-peak and thus not as high, so it would be easier to fit more NYC-bound trains, and the Boston-bound trains don’t really start getting to Boston until the AM peak is ending, and the passing track at Attleboro can help with that. The PM peak is harder, in that both commuter and HSR/Regional services peak at about the same time. But there’s a few things that can help with that: the three-track section between South Station and Readville, which can be extended to Route 128 on existing ROW with minimal effort will mostly get the Stoughton trains out of the way and let the Amtrak trains pass the MBTA commuters at Hyde Park. On the two track section south of Route 128, building high platforms and getting quick-accelerating MUs with a 100 mph top speed can save some time, and in the worst case, they’d have to run skip-stop service to keep the commuter rail’s average speed up and stay out of the way of the faster trains. This is a facsinating enough problem that I want to make some stringlines for timetables and see how it all works out in practice.

        • Alon Levy

          The issue is that 4+1 requires the exact same overtake infrastructure as 4+4, assuming the 4 tph are spaced evenly. Once 4 tph peak commuter traffic is desired – and as far as I can tell the MBTA is indeed planning on such traffic levels by 2030 – any intercity train will have 15 minutes, minus headways at both ends, to use shared track. What I said about having 11 minutes of time penalty on shared track I phrased in terms of a regional train between two successive intercity trains, but it’s equally true for an intercity train spaced between successive regional trains.

  3. Beta Magellan

    You mentioned additional stops at Back Bay and Route 128 as a way of slowing intercity trains, mentioning the trade-off between speed and ridership. Is there any reason to think that multiple metropolitan stations might help make up for speed losses, are they of typically only of marginal benefit?

    • Alon Levy

      To be honest, I don’t know the effect of stopping at Back Bay and Route 128 on ridership. I’m pretty sure Back Bay is negative and a little less sure about Route 128. My thinking is that people at thoe stations could take the sped-up regional trains and transfer. Under the one-overtake option, transfers at Providence between a regional train to/from Boston and an intercity train to/from New York are timed to take 2 minutes. Under a two-transfer option, it’s about 8 minutes, minus 1.25 per infill station south of Attleboro.

  4. ant6n

    How about a 3tph+3tph+3tph.
    -The first 3tph is HSR Boston-Providence+beyond.
    -The second 3tph is the Boston-Providence commuter rail, with some intermediate stops. This train and the HSR meet at providence, so after Providence it can continue as a local train.
    -The third 3tph is Boston-Stoughton, with many local stops, possibly including in Boston itself.

    the starting pattern at Boston is first the HSR, 90sec later the Providence train, then 90sec later the Stoughton train. The HSR catches up with the Stoughton train at Canton junction, where that one will move off to the spur (that station will probably need a flyover junction). At Providence, the HSR will have caught up with the Providence train, where they meet at the station. Since both trains stop there, a padding of 2min should be enough. So the Stoughton-local can loose 14/15 min between Boston and Canton, and the Providence train can loose 17/18 min between Boston and Providence – which is similar enough to your calculated running time differences that either taking out a couple of stops of the Providence train, or just run the HSR a tad bit slower should make this work.

    During off-peak, one could space out the schedule to create 2tph+2tph+2tph (i.e. 30min service for all trains). In that schedule one could fit super-express Boston-New York trains – i.e. in the morning along reverse commute slots.

    The Providence line, as you said, should be 55min. This allows the 3tph with 6trainsets. The newly added stations, if any, whould all be in the Providence area, mostly after the Providence stop, so that the meet with the HSR train is possible at that stop. This would essentially create an S-Bahn service in that area, which extends to Boston.

    • Alon Levy

      You’re right about my tl;dr habit in general, but this is one post that really has to be long, to flesh out the details that distinguish a workable plan from a half-baked one.

  5. URT

    after googling the definition of expurgate, I realise:
    a) I really just mean prioritise and simplify!
    b) I am guilty of flaming hypocrisy

    Still enjoying the blog – keep up the good works

    • Alon Levy

      You know, I didn’t think about it. But such service could be successful, if only because there’s no direct freeway competing with it. It shouldn’t muck up MBTA-HSR compatibility; it only shares tracks with those trains for 7.5 km, and that’s on a relatively slow segment, so even if it runs slower DMUs it can fit in between the other trains. Under the one-overtake option, MBTA and HSR trains would be within 2-3 minutes of each other near Providence, giving a Woonsocket service ample time to use the line and even make multiple stops in Providence and Pawtucket. Under the two-overtake option, there would be a shorter continuous empty time slot, but MBTA trains would stop at least at Pawtucket and Central Falls, reducing the speed difference; this option would also give very frequent Providence-Pawtucket rail service.

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  18. Levi Ramsey

    I admit that I’m not an expert on these (this post is as much about further information to refine things), but I’ve got a schedule that seems to be able to run at peak times 5 trains of Silverliner V-ish EMUs per hour between South Station and Mansfield, 2 such trains per hour between South Station and Needham, 3 Acelas per hour, and 3 regionals.

    The basics:

    MBTA stops running diesel inside of Mansfield by having all service to Mansfield facilitated by essentially merging the Franklin and Fairmount lines, electrifying the Needham line (the most SEPTA-ish line, definitely at least on the South side, in terms of typical distance between stops), and scheduling the Stoughton/Taunton/South Coast service to facilitate timed cross-platform transfer with Mansfield trains.
    MBTA subsidizes RIDOT operation of South Attleboro-Mansfield diesel service along the Providence line for at least 20 years via transfer of coaches and locomotives sufficient for RIDOT to provide Mansfield-Westerly service.
    Modifications made to Mansfield Station to allow for cross-platform transfer between RIDOT diesel and MBTA electric trains (from looking at Google Earth, that could be accomplished with as little as a third track to the west with a new bridge over Chauncy St and a reduction in parking spaces).
    8-car high-level platforms at all stations on the line

    Acela service on the present schedule seems to hit Mansfield about 22 minutes out of South Station; Regional at about 26 minutes. 3 of the Mansfield tph at peak are more express: South Station – Back Bay – Hyde Park – 128 – Canton Jct – Mansfield in 28 minutes. The other two are locals that also stop at Ruggles, Forest Hills, Readville (mostly for transfers with Franklin/Fairmount), and Sharon, reaching Mansfield in about 32 minutes. Needham trains hit Forest Hills at about 10 minutes. So this implies required spacings of about:

    12 minutes between Mansfield local and Acela
    10 minutes between Regional and Acela (with an overtake in Attleboro)
    8 minutes between Mansfield express and Acela OR Mansfield local and Regional
    6 minutes between Mansfield local and Mansfield express
    4 minutes between Mansfield express and Regional
    4 minutes between Needham and Acela, Regional, or Mansfield express

    Mansfield schedule coordination between MBTA, RIDOT, and Amtrak trains could be complex, but it seems doable (there’s benefits in this plan for all 3, after all).

    This makes the following model hour some value of “practical” at South Station to achieve hourly Acela, hourly Regional, 3 expresses an hour to Mansfield, 2 locals to Mansfield, and 2 Needham trains; spots where extra Acelas or Regionals could be added are noted

    :00 Acela
    :02 to:10 >>> POSSIBLE ADDITIONAL REGIONAL <<>> POSSIBLE ADDITIONAL ACELA <<>> POSSIBLE ADDITIONAL ACELA <<>> POSSIBLE ADDITIONAL REGIONAL <<<
    :52 Mansfield express

    Off-peak Mansfield service would be slightly less express (adding Forest Hills and Sharon), but (at least in daytime) keep the :12/:32/:52 pattern with no local service (if you needed to get from Ruggles to Franklin, you'd go inbound to South Station and transfer). MBTA ticketing would be improved to allow for free transfer from commuter/regional rail to subway and probably to encourage less time-sensitive trips to move to off-peak.

    The only major construction this requires is high-level platforms on the NEC stations (Needham line could be high-leveled at a later date) and the Mansfield work. An extra Acela round-trip to Boston (perhaps arriving South Station around 9 and departing around 7?) should generate about 500*$150 per weekday in Amtrak sales or about $20m a year, giving an NPV over 30 years of about $200m, enough for Amtrak to buy the MBTA 80 or so Silverliner V's to induce the MBTA to electrify.

    • Levi Ramsey

      Gah, the HTMLizer ate the proposed hour

      :00 Acela
      :10 POSSIBLE ADDITIONAL REGIONAL
      :12 Mansfield express
      :14 Mansfield local
      :16 Needham
      :26 POSSIBLE ADDITIONAL ACELA
      :30 Regional
      :32 Mansfield express
      :40 POSSIBLE ADDITIONAL ACELA
      :44 Mansfield local (would move to :42 if :50 Regional is added)
      :46 Needham
      :50 POSSIBLE ADDITIONAL REGIONAL
      :52 Mansfield express

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