Mixing High- and Low-Speed Trains

I stream on Twitch (almost) every week on Saturdays – the topic starting now is fare systems. Two weeks ago, I streamed about the topic of how to mix high-speed rail and regional rail together, and unfortunately there were technical problems that wrecked the recording and therefore I did not upload the video to YouTube as I usually do. Instead, I’d like to write down how to do this. The most obvious use case for such a blending is the Northeast Corridor, but there are others.

The good news is that good high-speed rail and good legacy rail are complements, rather than competing priorities. They look like competing priorities because, as a matter of national tradition of intercity rail, Japan and France are bad at low-speed rail outside the largest cities (and China is bad even in the largest cities) and Germany is bad at high-speed rail, so it looks like one or the other. But in reality, a strong high-speed rail network means that distinguished nodes with high-speed rail stations become natural points of convergence of the rail network, and those can then be set up as low-speed rail connection nodes.

Where there is more conflict is on two-track lines with demand for both regional and intercity rail. Scheduling trains of different speeds on the same pair of tracks is dicey, but still possible given commitment to integration of schedule, rolling stock, and timetable. The compromises required are smaller than the cost of fully four-tracking a line that does not need so much capacity.


Whenever a high-speed line runs separately from a legacy line, they are complements. This occurs on four-track lines, on lines with separate high-speed tracks running parallel to the legacy route, and at junctions where the legacy lines serve different directions or destinations. In all cases, network effects provide complementarity.

As a toy model, let’s look at Providence Station – but not at the issue of shared track on the Northeast Corridor. Providence has a rail link not just along the Northeast Corridor but also to the northwest, to Woonsocket, with light track sharing with the mainline. Providence-Woonsocket is 25 km, which is well within S-Bahn range in a larger city, but Providence is small enough that this needs to be thought of as scheduled regional rail. A Providence-Woonsocket regional link is stronger in the presence of high-speed rail, because then Woonsocket residents can commute to Boston with a change in Providence, and travel to New York in around 2 hours also with a change in Providence.

More New England examples can be found with Northeast Corridor tie-ins – see this post, with map reproduced below:

The map hides the most important complement: New Haven-Hartford-Springfield is a low-speed intercity line, and the initial implementation of high-speed rail on the Northeast Corridor should leave it as such, with high-speed upgrades later. This is likely also the case for Boston-Springfield – the only reason it might be worthwhile going straight from nothing to high-speed rail is if negotiations with freight track owner CSX get too difficult or if for another reason Massachusetts can’t electrify the tracks at reasonable cost and run fast regional trains.

There’s also complementarity with lines that are parallel to the Northeast Corridor, like the current route east of New Haven, which the route depicted in the map bypasses. This route serves Southeast Connecticut communities like Old Saybrook and can efficiently ferry passengers to New Haven for onward connections.

In all of these cases, there is something special: Woonsocket-Boston is a semireasonable commute, New London connects to the Mohegan Sun casino complex, New Haven-Hartford and Boston-Springfield are strong intercity corridors by themselves, Cape Cod is a weekend getaway destination. That’s fine. Passenger rail is not a commodity – something special almost always comes up.

But in all cases, network effects mean that the intercity line makes the regional lines stronger and vice versa. The relative strength of these two effects varies; in the Northeast, the intercity line is dominant because New York is big and off-mainline destinations like Woonsocket and Mohegan are not. But the complementarity is always there. The upshot is that in an environment with a strong regional low-speed network and not much high-speed rail, like Germany, introducing high-speed rail makes the legacy network stronger; in one that is the opposite, like France, introducing a regional takt converging on a city center TGV station would likewise strengthen the network.

Competition for track space

Blending high- and low-speed rail gets more complicated if they need to use the same tracks. Sometimes, only two tracks are available for trains of mixed speeds.

In that case, there are three ways to reduce conflict:

  1. Shorten the mixed segment
  2. Speed up the slow trains
  3. Slow down the fast trains

Shortening the mixed segment means choosing a route that reduces conflict. Sometimes, the conflict comes pre-shortened: if many lines converge on the same city center approach, then there is a short shared segment, which introduces route planning headaches but not big ones. In other cases, there may be a choice:

  • In Boston, the Franklin Line can enter city center via the Northeast Corridor (locally called Southwest Corridor) or via the Fairmount Line; the choice between the two routes is close based on purely regional considerations, but the presence of high-speed rail tilts it toward Fairmount, to clear space for intercity trains.
  • In New York, there are two routes from New Rochelle to Manhattan. Most commuter trains should use the route intercity trains don’t, which is the Grand Central route; the only commuter trains running on Penn Station Access should be local ones providing service in the Bronx.
  • In the Bay Area, high-speed rail can center from the south via Pacheco Pass or from the east via Altamont Pass. The point made by Clem Tillier and Richard Mlynarik is that Pacheco Pass involves 80 km of track sharing compared with only 42 km for Altamont and therefore it requires more four-tracking at higher cost.

Speeding up the slow trains means investing in speed upgrades for them. This includes electrification where it’s absent: Boston-Providence currently takes 1:10 and could take 0:47 with electrification, high platforms, and 21st-century equipment, which compares with a present-day Amtrak schedule of 0:35 without padding and 0:45 with. Today, mixing 1:10 and 0:35 requires holding trains for an overtake at Attleboro, where four tracks are already present, even though the frequency is worse than hourly. In a high-speed rail future, 0:47 and 0:22 can mix with two overtakes every 15 minutes, since the speed difference is reduced even with the increase in intercity rail speed – and I will defend the 10-year-old timetable in the link.

If overtakes are present, then it’s desirable to decrease the speed difference on shared segments but then increase it during the overtake: ideally the speed difference on an overtake is such that the fast train goes from being just behind the slow train to just ahead of it. If the overtake is a single station, this means holding the slow train. But if the overtake is a short bypass of a slow segment, this means adding stops to the slow train to slow it down even further, to facilitate the overtake.

A good example of this principle is at the New York/Connecticut border, one of the slowest segments of the Northeast Corridor today. A bypass along I-95 is desirable, even at a speed of 200-230 km/h, because the legacy line is too curvy there. This bypass should also function as an overtake between intercity trains and express commuter trains, on a line that today has four tracks and three speed classes (those two and local commuter trains). To facilitate the overtake, the slow trains (that is, the express commuter trains – the locals run on separate track throughout) should be slowed further by being made to make more stops, and thus all Metro-North trains, even the express trains, should stop at Greenwich and perhaps also Port Chester. The choice of these stops is deliberate: Greenwich is one of the busiest stops on the line, especially for reverse-commuters; Port Chester does not have as many jobs nearby but has a historic town center that could see more traffic.

Slowing down the intercity trains is also a possibility. But it should not be seen as the default, only as one of three options. Speed deterioration coming from such blending in a serious problem, and is one reason why the compromises made for California High-Speed Rail are slowing down the trip time from the originally promised 2:40 for Los Angeles-San Francisco to 3:15 according to one of the planners working on the project who spoke to me about it privately.


  1. wiesmann

    One case of “Speed up the slow trains” on shared tracks could be the Gotthard Base Tunnel, where freight trains need to run at 100 Km/h.

  2. adirondacker12800

    It’s a pity Long Island exists. It screws everything up. Try to keep two or three things in mind.

    • Borners

      The JR East Shinkansen network is a mix of speeds; both Mini-Shinkansen lines, the Seikan Tunnel-Hokkaido Shinkansen and the Omiya-Tokyo section is stuck at the upper end of convention-rail speeds. That branching from a city center terminus makes it less like the other lines with their HSR-as-subway strategies. Which is a little ironic given JR East’s Shinkansen clientele is the most commuter focused with Takasaki-Omiya-Utsunomiya.

      That diversity is also why JR Tokai is so against about ever linking its system to the JR East one for good reasons and bad . Right now pre-Maglev there is a good case that the Tokaido line is at capacity and adding timetable risk would go against that. Though I do think its also that with profits so high they can afford to get fussy and imperious their divergence in electronic safety equipment was gratuitous.

      • Phake Nick

        The Seikan Tunnel and Hokkaido Shinkansen are outside JR East’s management, although they’re indeed part of the network
        The mini Shinkansen lines in themselves aren’t that much of a problem since local traffic on those lines are low
        The Omiya-Tokyo segment was apparently built as such after JNR concluded that the soil around the area was difficult to tunnel through at that era and thus have to be constructed on surface, then against local NIMBY they signed momentum of understanding with local representative, mechanically guaranteeing the line couldn’t run at high speed by lowering the construction standard including the turning radius, in addition to the construction of the parallel conventional line the Keikyo Line.
        With the construction of Joetsu and Hokuriku Shinkansen following Tohoku Shinkansen, the proposal initially included a new terminal station from Omiya tunneling all the way into Shinjuku station. However, since the current slower line from Omiya to Tokyo have enough capacity to carry all the passengers and trains carrying them on all three lines despite lower frequency on Joetsu and Hokuriku Shinkansen, the planned new line to Shinjuku isn’t viewed as necessary, and it will cost a lot with such a long deep tunnel, thus low cost to benefit ratio, and splitting trains in JR East network into departing from two different stations, something like what South Korea is doing now, would also have negative impact on frequency of each individual stations, especially in term of trains heading to/from stations with fewer demand and thus receive fewer departures each days

  3. Paul

    I’m noticing that if all the high-speed lines on the map were built out, there could be two service patterns between New York and Boston: one via New London-Providence, the other via Hartford-Springfield. Switzerland has something like this between Geneva and Zurich, where the routes via Neuchâtel-Biel/Bienne or Fribourg-Bern are only a couple minutes apart in travel time. For anyone going end-to-end, it doesn’t really matter which route you take and there’s probably some reliability gain from having an easy alternative in case of service disruptions/special events/etc.

    • adirondacker12800

      Via Hartford will be slower. Great for people in Worcester, Springfield and Hartford but Boston-New York will be via Providence. Which is okay, there are enough people along the Inland Route to support service.
      There’s another one that never makes it onto the map. New York-Philadelphia via the former Reading-Central of New Jersey route. It would be slower than the NEC but faster, door-to-door for the people along it.

      • Steve

        When Amtrak last ran the Inland route in the early 90’s it was about an hour longer than the Coast route, though it’s actually only about 10 miles longer and serves a far greater population (about twice as many).

    • Phake Nick

      Really depends on how they decide to spend their money and which exact routing or tech spec they would follow, as well as choices made during planning or even construction and operation. These few minutes are easy to lose due ro speed deterioration

    • Steve

      The population along the Inland route is significantly greater than that of the Coast route. Taking just the populations of the largest cities on the routes, Providence and New London have about 207K people while Worcester, Springfield and Hartford have about 460K. Those number don’t take into account urban areas – the Hartford-Springfield urban area is nearly 2 million, while the Providence urban area is about 1.2 million. When Amtrak ran the Inland route it was less than 10 miles longer than the coast route.

  4. Onux

    Why would you have regional trains do Boston-Providence in 0:47? Shouldn’t the padded run time be 0:56 to allow for a takt with trains from Woonsocket/Worcester, hourly NEC HSR expresses, etc.

    • adirondacker12800

      There are two trains an hour, during the day, now. We aren’t going to spend a gazillion dollars for two trains an hour.

    • Alon Levy

      1. Projected demand on both regional and intercity service on Boston-Providence fills way more than an hourly train. The TransitMatters Regional Rail plan calls for 15-minute regional service off-peak, and those trains would be pretty empty but half-hourly trains would be full and almost as expensive to operate (peak service has to be 4 tph).

      2. South Station is not really a good location for a knot because of branching – Providence and Stoughton trains should run so frequently together that it’s not possible to set up a knot.

      3. The main constraint to slot into the takt is not the turnaround time, but overtakes if intercity trains are ever sped up beyond about 35 minutes.

      • adirondacker12800

        If the local train is on the local track the express train can do whatever it wants on the express track.

  5. Ernest Tufft

    The Renfe conventional slower speed line that runs on same electric overhead wire tracks as freight, with priority given to transit trains, and stops more frequently remains popular lower alternative to alto velocidad trains. Barcelona, Girona and Figueres have both transit train line systems, which provide great options for riders.

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