Gap Fillers

The United States is in the process of mandating an innovation commonly seen in Central Europe to guarantee train accessibility: the gap filler, also called the train-mounted extender. When there is a significant gap between the train and the platform, most passengers can still board fairly easily, but passengers who use wheelchairs may get stuck and passengers who have strollers, walkers, or heavy luggage may have difficulties. It is not always possible to reduce the gap to an acceptably narrow level, and therefore some trains have automatic gap fillers mounted on the train extending toward the platform.

What is the gap filler?

Here is a 10-second video of operations in Zurich. The gap filler is mounted on the train and extends over the platform, creating a continuous surface with gentle enough slope that people in wheelchairs can get on unaided. Without gap fillers, sometimes the train-platform gap is too wide and people can get stuck. If the gap gets wide enough, then even able-bodied passengers are at risk of falling through it.

There are also similar operations in Paris and various parts of Germany, though not Berlin. European railroads even use gap fillers when there is no level boarding, to prevent people from falling into the gap between the train and the platform, or to create an external step if the same train serves platforms with different heights one or two steps apart.

Why not just build trains with shorter gaps?

Train widths are not standardized in Europe – the loading gauge in theory permits trains to be 3.15 meter wide, but this is net of curves, so a rigid carbody always has to be somewhat narrower, especially if it is long. That by itself bakes in 10-15 cm gaps.

Two additional effects can create gaps. First, if the train platform is on a curve, then the distance between the most distant point on the train and the platform must increase even if the loading gauge is not defined on a curve. Second, wheels wear out over time, which may create a small vertical gap; if the vertical gap is more than about 2 centimeters then a substantial minority of wheelchair users can’t traverse it (see Barcelona’s universal accessibility plan, PDF-p. 14), and if it is more than 4.5 cm then a majority can’t. Even metro systems, which have level boarding, sometimes have big gaps because of these two effects, requiring manual bridge plates that lengthen station dwells.

Gaps and the United States

The American loading gauge is far more standardized than the European one, since the US is one country and Europe is not. Nonetheless, large gaps exist, for multiple reasons:

  1. The standards for platforms include generous margins: the distance between the track center and a high platform is by law 5′ 7″, and a train is at most 10′ 8″ wide (usually 10′ to 10′ 6″), so the laws already require gaps of at a minimum 3″ (76 mm, about the maximum passengers in wheelchairs can reliably cross) and often 4-7″ (10-18 cm).
  2. The American loading gauge is defined on straight track. Curved platforms require larger horizontal gaps, and as a result many agencies prefer not to build curved platforms at all, even where it is the best design compromise.
  3. There is some amount of oversize freight; the military wishes for a network with generous enough loading gauge to carry tanks.

Gap fillers were unfortunately unknown until recently. MassDOT even used the need for oversize freight as an excuse not to raise the platforms on commuter trains. Instead, American solutions included expensive gauntlet tracks or just keeping platforms low and inaccessible.

Fortunately, once an American implementation of the gap filler existed, namely on Brightline in South Florida, American regulators learned of the existence of this technology, and are now considering mandating it.


There are two conclusions from this story.

The first is that gap fillers are a good technology and more passenger railroads should use them to improve accessibility, not just for passengers in wheelchairs but also ones with strollers or luggage or who are at risk of falling through the gap. The US should aim for universal adoption of this technology nationwide.

The second is that once a good public transportation innovation does reach the United States, it can spread nationally more easily, as globally incurious but nationally curious administrators have a domestic example to look at. This is an example with train-mounted extenders, but the same may be said of fare integration, clockface timetables, lightweight EMUs, and so on. The first agency to adopt any such measure can expect visits from other agencies aiming to learn from its success.


  1. Bgriff

    Not really on topic, but I have been wondering and your details on level boarding made me think of it: in NYC, “accessible” subway stations have a raised section of platform near the center of the train that’s usually actually level, and then the rest of the train is usually a decent gap to actual level boarding. Is there any good reason besides laziness and insane costs that they don’t just make the whole platform that slightly higher level? Are some rolling stock types at an entirely different height or something?

    • Alon Levy

      New York’s motto on accessibility is “millions for station beautification, not one penny for disabled people.” The extent of aggressive neglect of accessibility in New York is staggering, and you can see this in how the ADA program is sandbagged, with way more spending per station than just the elevator costs.

        • Alon Levy

          Yeah, sure, but still, in Boston nearly the entire cost of an ADA retrofit is the elevators whereas in New York less than half is, because the MTA sandbags these projects.

  2. Gok

    Gap fillers are good.

    The only think that gets American transit agencies to adopt new technology is a legal mandate, and legal mandates only happen when people die (which is what got PTC to happen for example). People do die from platform gaps though; someone was killed just a few days ago in Chicago. So eh it may have a shot.

    • Herbert

      Wouldn’t “small investment that increases revenue / reduces cost” also be an argument to do something even without legal mandate?

      • Richard Mlynarik

        No. Never. American “public” transportation “professionals” only ever propose and promote projects that involve massive capital expenditures and increased operating costs.

        The system exists solely to reward consultants and employees.

        “Increase revenue / reduce cost” is something that is stated as a justification (fare gates! electrification!), but never occurs, because burning money is always entirely the overriding purpose of every project.

        It really is that bad, and the people involved at every level really are that corrupt and self-serving.

          • Richard Mlynarik

            I’ve been watching the good lower level people not be allowed to get anything at all done for 30 years in and around Boston and San Francisco. Some nice people. Some smart people.

            They burn out or drop out or (who can blame them? “Forget it, Jake. It’s Chinatown.”) cash in.

      • Nilo

        The people who got them installed on Brightline wanted to do it on NJT, but it got vetoed by management. American passenger railroads as Richard points out do not have a good record or trying to reduce operating costs.

        • adirondacker12800

          Why would Florida East Coast be interested in New Jersey? Other than Conrail is moving their customer’s stuff on-time?

          • Alon Levy

            Because they’re American and they were reaching out to other American passenger rail officials for ideas?

          • Nilo

            Because they needed to hire people with experience running a passenger railroad? This isn’t a hard fact to verify Adirondacker, there are many articles discussing how they hired a lot of NJT staff, and this one from Bloomberg is where I got my claim.

            From the article:

            One of their early suggestions was to include a device on cars with a metal plate that would bridge the gap between the train and the platform. The public-transit contingent had seen briefcases and even small children disappear into the gap at Pennsylvania Station in New York. Even so, Tim Leiner, now assistant chief mechanical officer for Brightline, says his bosses back then were loath to do anything about it. “We actually had companies come in with a prototype,” he recalls. “It was right away: ‘We’ll never be able to do. Too many stops.’”
            Goddard, on the other hand, embraced the idea. “You can basically roll onto our trains with a wheelchair or a stroller or a suitcase,” he says. “These guys came up with lots of things like that.”


          • F-Line to Dudley

            At the intermediate stops where there’s no turnouts, Brightline’s full-high platforms have a noticeably larger gap ( than Northeastern pax rail ( Gaps in most of North American 48-inch territory are closed to the tolerable minimum by 2-3 inch thick platform edging (usually wood or composite so it can take bumps and dings expendably), and are more or less an ironclad requirement for commuter rail operators building full-highs because nobody has a complete homogenous fleet of auto- bridge plate cars. Wheelchairs can usually power over the 1-2 inches of remaining gap just fine from any old commuter car, and conductors only pull out the manual bridge plates for complete gapless passage upon request.

            Brightline’s different because its owner Florida East Coast is the largest non- Class I freight carrier in North America…to the point where they’ve continually lobbied the feds to keep adjusting-up the $$$ definition of what makes a Class I carrier so they can keep their biggest-of-Class II’s designation. There’s way more high-and-wide daily freight moving past those Florida platforms than nearly everywhere in Northeastern pax territory, because the continuity of pax service in the Northeast through the postwar wipeout years meant the freights retained their most-critical bypasses away from pax traffic traffic. It’s isolated, incidental overlap on only a few lines up there. The FEC, on the other hand, runs monster freights all up and down Brightline.

            That required a different strategy. Because Brightline was buying all-fresh rolling stock, they could equip their Siemens Viaggio Comfort coaches with vehicle-side platform extenders and not have to worry about accommodating a 2013-built Bombardier MLV and a 1977-built Arrow III with the same infrastructure like NJT and every other operator with large, heterogeneous fleets has to. So every Brightline platform situated on mainline trackage was built without gap-filler edging for a larger gap than any known 48-inch platform in the Northeast. Being able to do it vehicle-side in one purchase saved them loads in capital construction from having to play lineside freight-passing games, which was critical to the service meeting its startup budget.

            Amtrak will soon award bids for its Amfleet replacemen…presumably for the same exact Viaggio Comforts that Brightline has (since that’s what they bought as the Take Two procurement for Midwest/California coaches after the Nippon-Sharyo bi-level order collapsed, that’s what VIA Rail is ordering for the Canadian Corridor, and they’re fast becoming a 100% Siemens shop on locomotives). That opens up great potential for state-sponsored Northeast routes to at long last build full-highs in freight clearance territory without need to do passing tricks. Pennsylvanian west of Harrisburg (major Norfolk Southern mainline), Downeaster north of MBTA territory, Vermonter, Adirondack + Ethan Allen Express north of Saratoga Springs…those can all be done as gapped full-highs with the new fleet. So can the ittiest-bittiest Empire Service stops like Rome and Amsterdam if NYSDOT wants to save money punting second platforms w/ freight passage off till later (overall Empire Service is dense enough to require gapless full-highs, which is what they’ve been building).

            It won’t matter much for commuter rail because gapped platforms do come with a slight dwell penalty for the car-side mechanism to deploy, so house standards that currently call for those 3-inch gap fillers for all full-high construction should NOT be relaxed to encourage more laziness. There simply aren’t nearly enough platforms hosting high-and-wide clearance freight in the Northeast to drive a policy change there. Most of the malingering lows and mini-highs out there are on NON clearance routes. With many of the exceptional cases that do need to accommodate freights already being high-traffic enough to merit full passing solutions rather than platform gap tricks…solely on the merits. Rather, you can consider gapped full-highs a last resort for the small handful of very hard-to-stamp-out toughies. For example, Ballardvale and Andover on the MBTA Haverhill Line have current lifetime exemptions for mini-high accessibility from the Massachusetts Architectural Board (whose state-level accessibility regs are otherwise the toughest in the nation) because those sites are too constrained for extra tracks for the heavy Pan Am freight traffic, and their positions abutting grade crossings make gauntlet tracks impractical. There’s charitably maybe another 2-4 stops on the entire MBTA commuter rail that could *ever* qualify for similar exemption…as most of the time the M.A.B. takes the severest interpretation and says “Build the full gauntlet or passer” (…and then the T artificially delays it to get out of the cost). Gapped full-highs would be a way to get those raised, at a cost of the T just needing to gerrymander fleet assignments of uniform auto- bridge plate consists to that one schedule. Not perfect, but an equitable solve for the last tough remainders. Similarly, MARC can look at this equipment gerrymander for doing up the Camden Line with gapped full-highs, as can Metro North with the Port Jervis Line. There aren’t any other whole lines of similar scope I can think of…usually just a couple spot stations that happen to be at an incidental point of freight overlap. But similarly it can be a last resort for stamping out remainders so long as it isn’t perverted into a lazy kludge (i.e. commuter rail NEEDS the platform-side gap filler for idealized dwells anywhere/everywhere it’s feasible).

          • adirondacker12800

            So FEC hired people from NJTransit that NJTransit wanted to get rid of? Almost 900 cars in NJtransit’s fleet, last time Wikipedia counted, times three sets of doors per side and figure out how to do it the stations that still have low platforms… it’s probably a good idea to let the people who have no concept of the scale of the place they are working at, work at big amusement park ride in Florida?

          • adirondacker12800

            Ballardvale and Andover on the MBTA Haverhill Line……and their positions abutting grade crossings make gauntlet tracks impractical.

            What happens when they get around to grade separating it???? . . . Very quick glance at the satellite views it could even be three tracks wide. Unless the parking lots surrounding the tracks have great historical and cultural value.

          • F-Line to Dudley

            Wetlands and adjacent street intersections pinch Ballardvale and Andover such that there isn’t enough linear room to do anything over the full 800 ft. length of a regulation MBTA platform, and they’re both in vibrant and walkable village centers so there’s limits to how many land-use kludges are too much in pursuit of a singular goal. They definitely won’t ever be grade separated the way street grid and wetlands align around the ROW.

            So…not many practical options. Gauntlets are not reliable through grade crossings whose flanges already accumulate enough winter gunk in a cool/wet New England climate and would constitute an elevated derailment risk on the extra crossing flanges. That boils it down to (1) keep the current exemption for retractable-edge mini-highs…frustrating, but if this is the literal only MBTA schedule that will permanently be stuck flipping door traps also a pretty minor concession in the grand scheme. Or, do gapped full-highs, make sure their next fleet purchase of 200+ coaches and any future EMU’s to-be-determined come factory-ordered with vehicle-side gap fillers, and take requisite pains to run uniform gap-filler sets on all Haverhill schedules (while literally everything else on the system can be a mixed consist).

            In the end, gapped highs + gerrymandered equipment assignments are probably the most satisfactory answer. The ‘sloppiest seconds’ ends up just a handful of seconds’ dwell penalty while the gap-filler mechanism flips rather than having to hoof it upstairs forever or overcrowd the 1-car mini-high and fight your way through multiple cars inside to get a seat. Policy-wise they just have to ensure that gapped platforms aren’t an invite to laziness and more punting-off of other projects where they know full well they need to build real passing tracks (like the outer Worcester Line intermediate stops if you want level boarding compatibility AND robust compatibility with layer-cake scheduling of clock-facing overtakes per Alon’s post of last week). And as previously noted, gapped highs are also a solve for MNRR Port Jervis Line and MARC Camden Line, two of the extremely few Northeastern commuter routes that have to square clearances at MANY consecutive and majority-overall stops instead of just single square-peg outliers like aforementioned Ballardvale & Andover. Ridership on the meandering Port Jerv and Camden are low enough that those routes are never going to demand overbuilt passers and will always be behind much higher-priority routes in pursuit of accessibility funding. But if you likewise could just mass-raise the platforms as gapped full-highs and gerrymander one schedule’s worth of equipment assignments to square it…that ends up a path forward for getting level boarding completely and quickishly implemented on those low-margin routes where other forces are simply not going to compel those agencies to get it done before the heat death of the universe.

          • Alon Levy

            The MBTA is thankfully not doing gauntlets anymore. Some parts of the agency did realize it’s not 1952 anymore.

            But also, what the fuck does “priority for accessibility funding” even mean? This isn’t a village, it’s a metropolitan area the size of Berlin (Boston) or the combined sizes of the Rhine-Ruhr, Berlin, Frankfurt, Hamburg, and Munich (New York). Raise all the platforms, don’t try to gerrymander who gets accessibility and who gets Aktion T4.

            EDIT: one probably stupid thing that makes me like gapped high platforms is the possibility of slowly converting the entire suburban network to oversize clearances, allowing 3.66 m wide trains as in India.

    • yuuka

      People die from getting pushed onto tracks all the time, so why hasn’t the FTA legally mandated platform edge gates yet?

      (my inner devil tells me that’s yet another way to put a halt to transit projects)

        • Richard Mlynarik

          Not so! Platform edge screens are easier for BART than any other US system — I’m not sure what you’re on to with “non-standard door locations”.

          BART train control pretty much won’t allow trains doors to open except within close-enough (maybe 20cm tolerance? can’t find my references right now) alignment to platform berthing fiducials even today. The train fleet is transitioning from a uniform 2-door per 70 foot (feet! how quaint!) to uniform 3-door per 70 foot (non-articulated! how nostaligic and retro and low capacity! how USA USA USA USA USA USA USA!) train fleet. All the actually hard stuff is in place already, and has been for 30 years.

          Aside from the criminal (literally criminal) costs of USA USA USA USA NUMBER ONE public works contractors and consultants, there’s no obstacle to platform edge doors on BART. I’m not saying it should be the agency’s highest priority, but it’s one that would be very simple to implement (in terms of little things like train control and civil engineering) if BART weren’t in the USA.

        • Nilo

          My understanding was BART’s two door and three door fleet mix was the problem right now. Obviously once the transition to 3 doors is done the whole thing should be easy.

          As usual the ridiculousness of US rolling stock procurement prevented them from buying true walk through trains, but honestly I always thought the easiest capacity fruit on BART was not having such enormous seats. The trains are huge as it is compared to its worldwide peers. Does any system that pretends to be a metro system actually use bigger trains?

          • Joey

            BART’s system is smart enough to announce whether an approaching train is 2 or 3 doors per car, it can figure out which doors to open. The doors on the new cars are in the same places, there’s just another one between them.

    • Jon

      Legal mandates aren’t the way to go. If an idea is great the market, or a market, will adopt it. Holding a gun to one’s head is not a solution, except in the case of something that is sensible and increases choice, such as accepting cash. When companies/agencies go the cashless route it hurts everyone.

      • Nilo

        If American Railroads were at all sensitive to market desires they’d be running way more off peak service, and cutting conductors. But there is no free market in transit service, and mandating stepless entry either via smaller platform gaps, or gap fillers is logical.

  3. Eric

    “wheels wear out over time, which may create a small vertical gap;… and if it is more than 4.5 cm then a majority can’t.”

    A whole 4.5cm of the wheel can be eroded away and the train still be in use???

      • Eric

        I’m not sure which part of the page I should be looking at?

        I guess the key fact is that the wheel gets worn away in normal reuse, then they send it to the shop to be reground into its original shape (but with smaller diameter), and they can do this repeatedly, so over time the wheel gets much smaller but it always has the needed shape?

      • Onux

        Don’t modern trains address the vertical clearance issue with pneumatic suspensions that keep the floor at the same level regardless of load and wheel wear? The same way some modern trains can estimate passenger load from the greater force on the pneumatic suspension as more people get on.

        • Coridon Henshaw

          Automatic level compensation for passenger loading has been around since at least the mid 1960s. I don’t know if automatic compensation for wheel wear is common or available. It seems like a much harder problem to solve reliably, however, as it requires some way to accurately detect the wheel diameter (or the surface of the rail) that can’t be tripped up by the generally awful sensor environment under rail vehicles. Getting the car height wrong because rat ran under the train and confused a rail height sensor would be bad.

          • Eric

            You could just measure the wheel diameter once a month and update the value accordingly…

          • Richard Mlynarik

            Wheel wear rate is usually quoted in units of mm of diameter per 10^5 km.
            10^5km is on the order of half a year to a year in service for commuter/regional equipment or four to six months for HS trains — and that’s assuming non-USA non-shit levels of equipment utilization.
            Wheel reprofiling is usually done when diameter wear aproaches 5mm, and reprofiling cuts are on the order of 5mm diameter. Every couple years.
            So there’s no call for monthly ride height adjustment, more like six-monthly wheel profile inspection. (More for HS trains.)

          • adirondacker12800

            But but but re-calibrating the distance once a quarter when it’s in the shops for other things is no fun. Doing that doesn’t involve multiple sensors that can get muddy or snow covered. Or snag a piece of litter. Or break down.
            …… To platforms that aren’t in the same place twice because there is weather.

        • F-Line to Dudley

          Vertical level is maintained by the under-car air ballast, whose primary purpose is to smooth out the ride by dampening vibrations with a cushion of air. It’s entirely self-regulating via simple air pressure exchange, so the level interface does not end up varying even as the car goes through heat-up/cool-down cycles over the course of a trip. They’re pretty dirt-simple mechanisms that have been around for a century.

          A leaking air ballast will be instantly recognizable by the much louder and rougher ride, and car that can sag up to several inches below the platform level. If that effect becomes too pronounced during the course of a trip staff may isolate the car, as it’s uncomfortable and a tripping hazard upon egress but does not impact any of the other cars in the consist.

          It is possible to adjust the air ballast for differing platform heights. The previous generation of Hawker-Siddeley HRT cars on the MBTA Blue and Orange Lines were mechanically identical (the Orange 01200’s, still malingering in service, even have disused pantograph hookups on the roofs like their retired Blue 0600 counterparts) and only differed by larger Orange vs. smaller Blue dimensions. About 15 years ago the T floated a plan to send the entire Orange fleet and one-third of the Blue fleet through complete midlife overhaul and to bring the Blue cars onto Orange as an expansion fleet. The Blue cars are 16.5 ft. shorter, one set of doors fewer, and interface with slightly lower platform height…but are the same width. The Blue 0600’s would’ve trainlined as set lengtheners comprising 2 cars in every 6-car set bookended by 4 native-Orange 01200’s, and had their air ballast adjusted up to higher pressure to square the platform heights. Repurposement plan was scrapped when the T found too much aluminum carbody corrosion in the Blue fleet from all those years of running along the oceanfront in Revere, but technically it was fully feasible.

          To my knowledge there aren’t any on-the-fly ballast adjusting trainsets anywhere in the world for squaring different platform heights (in inches on high-vs.-high platforms, not feet like high-vs.-low) on the same trip. Mostly because it’s such exceedingly rare coincidence to have such small-scale height differences on the same network that don’t also come ensnared simultaneously in more problematic car width differences. But it is technically possible to do a ballast raising/lowering in-motion in the span of one stop with air compressors and computer guidance.

  4. chris t

    One question I’ve had for a long time — why are gap fillers always train-mounted? It seems like a robust extension would be easier to implement on station platforms.

    • Alon Levy

      Platform-mounted gap fillers are less reliable. Platforms are not supposed to be mechanically complex things – they’re supposed to be slabs of concrete.

    • threestationsq

      Trains have to go to a central location for maintenance on a regular basis anyway. Sending a crew out to do maintenance on a safety-critical element of a station platform is much more overhead, especially as it would probably require disrupting service while they did it. (Think about how often station escalators and elevators are out of order for maintenance, to the point that some guidelines now recommend having multiple elevators so there’s a backup.)

    • YDD

      In addition to the above, door mounted extenders will always be at the door. Platform mounted ones would require the train to stop in exactly the right place. That’s technically possible (for example when there are platform boarding gates) but such precision is not common on heavier lines.

        • chris t

          This is exactly how I imagined it. Maybe with some kind of light barrier to keep people off while it moves.

          Okay, so they do exist, and have for a long time. I suppose the fact that they’re not widely used suggests that the points above regarding maintenance are compelling.

          • adirondacker12800

            They painted “stand clear of moving platform” on the non moving part. There’s no barrier.

            They realized it was a bad idea and it wasn’t used anywhere else. And all the money they thought they were saving has been spent on it since they made that compromise.

        • michaelrjames

          I would have thought liability issues and their astronomic costs in the US would have mandated gap-fillers yonks ago. This suggests that it must have been tested and the courts must have found it is passenger beware, at their risk? Hmm, taking it one step further this begins to explain the generally awful state of so much public infrastructure in the US? Even, why it seems impossible to make and distribute just 1% of the COVID-19 test kits that the rest of the world has seemingly managed (including Iran … maybe Donald could do one of his famous deals with the mullahs, a swap …:-).

          But Alon, I can’t remember any gap-fillers on the London Underground where the “Mind the Gap” warning originated? (On the severe curve of the Northern Line, the world’s first true deep underground metro (1890), when its southbank loop was later extended further south, without straightening and using part of the loop for a new station with a strong curve.) I’m pretty sure the few stations in Paris with very tight curves (Bastille and Rapée?) don’t have any provision other than warnings. Maybe it is less of a problem with the shorter carriages?

  5. Herbert

    Gap fillers have been employed at various times in Berlin – on the U-Bahn. The network has two different loading gauges, one more narrow for U1 – U4 and one wider for all other lines. Sometimes due to acute rolling stock shortage on the wider loading gauge network, rolling stock is repurposed and fitted with so called “Blumenbretter”

  6. Walter Daum

    Gap fillers were unknown until recently? In NYC the 14th St station on the Lexington line has had them for decades if not from the start.

  7. adirondacker12800

    American solutions included expensive gauntlet tracks or just keeping platforms low and inaccessible.

    Does the gap filler fairy install and maintain them, for free?

      • adirondacker12800

        That doesn’t make them free. If you don’t have them they don’t have to be installed, inspected. repaired and during the major overhaul, replaced.

        • Herbert

          They cost less than the stupid “can only run in the U.S.” trains that the FRA mandates or mandated…

      • F-Line to Dudley

        If it’s an EMU or coach with quarter-point or midpoint doors, you pretty much need to have a vehicle-side gap filler solution handy to manage platforms with any tangible degree of curvature in them. End vestibule doors will match up fine to a full-high curved to maximum tolerances, but forget about opening a Shoreliner IV’s middle doors at a curved platform and forget about doing up New London’s long platform as full-high and being able to berth an M8’s quarter-point doors at it. NLN is only going to be able to accommodate M8’s on Shore Line East via construction of a stubby mostly-tangent high south of the S. Water St. grade crossing a little underwhelmingly offset from the main station. Not even the current stubbier high at that station used for berthing Acelas is straight enough for taking quarter-point doors gap-free.

        While tangent platforms are always something to shoot for whenever possible, if you do have incumbent curved platforms on a system that can’t plausibly be nip/tucked onto more tangent dimensions, transit agencies will need to think more about vehicle-side augmentation if additional doors are high-leverage procurement targets. Or…an agency that desires a little more flexibility for greater curvature in platform installations to expand its range of fittings will want to look at gap fillers on their fleet’s non-vestibule doors as a means of expanding the permissible range of platform construction.

        • adirondacker12800

          The demand in New London County isn’t downtown New London, it’s out by the casinos. New London’s solution is to move the platforms a whole block to the place where the tracks are straighter.

  8. ckrueger99

    So, gap fillers can be retrofitted to existing stock. e.g., my local (Philadelphia) SEPTA Silverliner Vs? This would allow high level platforms at any station, even ones on the Amtrak mainline or elsewhere where occasional freight traffic occurs?

    • adirondacker12800

      They don’t have them on the stations on the Trenton or Wilmington line that do have level boarding, now. Why would they suddenly need them?

      • ckrueger99

        I had heard that the reason why high platforms hadn’t been installed at certain stations on the SEPTA network was because of occasional freight on those lines. I’m trying to learn what is the hold up here, so if you have further info, let me know.

        • F-Line to Dudley

          On SEPTA the only places with high-and-wide traffic are:

          (1) West Trenton Line between Neshaminy Falls and West Trenton, overlap with CSX. Pre-existing tri-track passers at 3 of 5 stops…low-level Yardley + West Trenton the only ones that would need any accommodation. One of the exceeding few places in the U.S. where you can watch double-stacked freights travel underneath electrification. Note that NJT’s West Trenton Line proposal, which can potentially interline NY-Philly like the old Reading RR days–would fresh-build all of its new NJ intermediate stops as full-highs with passers.

          (2) Fox Chase Line between Newton Jct. and Lawndale, spot overlap with different segment of same CSX main that hits West Trenton. 2 single-platform stations–Olney, Lawndale–affected IF and only if service ever increases enough to require double-tracked platforms. As of today it’s OK as-is because the single platforms all have passers.

          (3) Norristown Transportation Center Station (low-level) on Norristown Line. Extreme small-distance overlap with that stop being all that stands between two diverging Norfolk Southern freight-only branches.

          So, no, SEPTA does not have any clearance excuses for being the Northeast’s #1-by-a-mile laggard in platform accessibility. They’re simply lazy and institutionally way more broken than any of their Northeastern commuter rail counterparts when it comes to capital spending on basic-most station upkeep. Which is way more an indictment of just how hopelessly far behind they are than any sort of endorsement of their still quite awful neighbors. They legit need to be gutted from within to make level boarding less of an utter anti-priority.

          With 3 stations…and a max of 5 if Fox Chase frequencies merit…ever impacted by freight clearances, there’s no reason for SEPTA to retrofit any Silverliners or even spec gap-fillers for new cars. It’s that much easier to solve with one-and-done freight passer or gauntlet renos to any of those 3-5 stations than pursue any vehicle-side tricks. Nearly all of their highest-leverage system expansion territory–like West Chester and Reading service restoration–has no clearance considerations. Now, if they wanted to tap some expansion opportunities in diesel territory by plowing west of Norristown T.C. via the Norfolk Southern Lehigh Line or doing circumferential service on the NS Morrisville Line…that could change things. But only on the push-pull, not EMU, car fleet as those freight mains wouldn’t be easy electrification targets and would likely be run with some acquired dual-mode locos heading up the regular push-pull fleet. But that’s just about the only possible scenario where it would come into play…and it’s a very limited one.

          • Alon Levy

            Those push-pull trains create more problems (schedule problems on the electrified trunk because the fleet loses its uniformity) than they solve (a little bit more coverage).

          • F-Line to Dudley

            Yes…which is why a poke on the Lehigh rates way, way low on their expansion bucket list below West Chester, Reading, and even the lukewarm Phoenixville proposal on the ex-Pottstown Line. They’ve halfheartedly studied a couple such Lehigh expansion scenarios, but none of them had much juice on their merits.

            Because of that diesel pokes aren’t likely to be a real-world planning dilemma for them until they’ve closed out a whole lot of other higher-leverage system expansion projects in all-electric territory. So the question is more a “what if?” and “what is/isn’t appropriate?” for retaining any push-pull presence on the system. If constrained exceptions like that were the only place SEPTA rationed push-pulls, they wouldn’t be so problematic. Un-electrifiable territory like the Lehigh could go on the board, they could partner with NJT for Philly-NYP run-thrus via West Trenton, or jump-start some other low-hanging fruit at managed risk. Stuff that’s pretty clearly a small subset of service, a small enough subset that it would (and would be expected to) stay out of everyone else’s way or cede priority at peakmost load, and which enables service that probably wouldn’t be plausible to mount by other means. Narrowcasted as just another tool in the toolbox for reaching the places where the EMU’s don’t/can’t reach soon enough, that’s an appropriate net-positive role that’s quite a bit more limited than today.

            SEPTA just refuses to see it that way. It’s this insane insistence of theirs that P-P is a “capacity enhancer” for rush hour, now doubled-down upon for another procurement generation, that screws them up. And makes one wonder if anyone with firing neurons is in charge there. The very worst time of day for P-P sets to be out in their greatest numbers is at rush, deployed on nearly all lines regardless of line-by-line elasticity for sorting around slower trains. They actually see that as a ‘feature’ to clog up some single-track branch with one of those sets at 5:00pm. Hopefully this mentality dies a merciful death when the Silverliner IV’s are replaced by their NJT-laundered option order of Bombardier MultiLevel EMU’s. While those things are not going to do SEPTA dwell times any solid given what extreme glut of low-platform stops malinger on their system, the MLV EMU’s are at least somewhat immune to car shortages by being pluggable with anyone’s rented stock MLV coaches sandwiched in a set around the EMU power packs. It’s a ticket out from under P-P rush hour hell if they choose to take it. Unfortunately they have their new CRRC push-pull bi-level order proceeding full speed ahead when those AREN’T trainline-compatible at all with the incoming MLV EMU’s, and there are too few total CRRC units on-order to plausibly re-sell to another agency (like they very well could offload their new Sprinter locos onto Amtrak at market rate). So they’re probably going to keep spewing the same utter BS for another 15 years that rush-hour P-P’s are somehow necessary and a “feature” instead of working to get out from under that albatross.

            As ever, SEPTA sets the incompetence low bar for everyone else to look less-awful by not undercutting.

  9. johndmuller

    The first example seemed a bit on the flimsy side and didn’t look like it would extend very far. The Brightline one seemed quite substantial and lengthy (although I think I’d like it better if there were some sort of fail-safe part of it resting on the platform itself (like a thin plate at the leading edge), rather than the entirely self supporting, abutting edge approach. As it is, I could see one losing it and just flopping straight down, along with someone’s foot.

    Brightline has only a handful of trains, each with a handful or so of cars, each with a handful or so of doors. NYC has hundreds of trains, a large majority of them with about 10 cars, each with 4-6 doors (which eyeball to be substantially wider too). That is a lot of extender$.

    It is not all that rare to see malfunctioning doors in subway cars; these would presumably fail at similar rates. The extenders would need to be hooked into whatever interlocking there is that keeps a train in the station if those doors aren’t all completely closed too, otherwise there would be rogue extenders chopping off signals supports and doing other mischief. Trains still run when a door is stuck closed on one or both sides; someone would have to decide whether a stuck-retracted flaw was a train-stopper or not.

    Regarding the vertical alignment, if one looks at the door-edge when a fairly well filled train arrives at a major station and a lot of people get off, the edge can go from an inch or more below the platform to an inch or more above it as it empties. Same in reverse as it fills, just due to the trains suspension system and the weight of the passengers,

    • adirondacker12800

      ….they run when the door is stuck open too….
      The gauntlet track is stuck in the wide position at one station the trains can skip that stop until the problem is cleared. An extender gets stuck, extended, things come to grinding halt all along the line until it’s cleared.
      The suspension moves up and down depending on the load and the suspension is quite springy when it’s new and not so much when it’s old. And wheels get trued and all of this stuff goes in the real world..

      • Herbert

        They somehow don’t have this problem on the automatically run Nuremberg subway lines U2 & U3. Where they don’t even have a driver who could intervene if need be…

        • adirondacker12800

          That you hear about. Doors stick closed, doors stick open. So do moving platform edges or moving thresholds. Just like the electricity will go out sooner or later or the signals will get very very confused.

          • Herbert

            I’ve been stuck in one of those trains for a few minutes on open track a couple of times. The gap filler falling to retract was never an issue

  10. yuuka

    Strictly speaking they’re not commuter trains, but the Mini Shinkansen in Japan have little flaps that come up as the train stops.

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