The Metro-North Accident and Train Control

Early in the morning on Sunday, a Metro-North train derailed on the Hudson Line, immediately south of the junction with Amtrak’s Empire Connection: maps of the derailment area can be found on the BBC, while The LIRR Today has a map and a diagram with speed limits. Four cars overturned, and four people died while more than 70 others were injured. The train was going at 82 mph (132 km/h) through a tight curve at Spuyten Duyvil with a 30 mph limit; the speed limit on the straight segment before the curve is 75 mph according to Rich E. Green’s map, which may be a few years out of date, and 70 mph according to the first New York Times article about the derailment. The curve radius appears to be 230 meters on Google Earth, putting the lateral acceleration rate at 5.8 m/s^2, minus a small amount of superelevation (at most 0.8 m/s^2, or 125 mm, to perfectly match the centrifugal force at the curve’s speed limit, and likely lower); the cutting edge of tilting trains allows about 2 m/s^2 lateral acceleration (see PDF-p. 2 of this article about the Pendolino), or 300 mm cant deficiency.

Initial reports of a mechanical brake failure seem unfounded: a National Transportation Safety Board briefing mentions that the brakes had functioned properly on brake tests and at previous stops on the journey (starting at 00:40 in the video). The focus is now on human error: the NTSB refused to say this outright, but beginning at 03:00 in its briefing video it trumpets positive train control as something that “could have” prevented the accident. Rick Gallant, who led California’s rail regulatory agency at the time of the 2005 Glendale crash, is also quoted as saying positive train control “probably could have” prevented the accident on NBC. Moreover, the train driver is quoted as having told investigators “he had become dazed before the accident, suffering what his lawyer referred to as ‘highway hypnosis.'” Metro-North’s spokeswoman made the strongest statement: “if the accident was caused by speeding, positive train control would have stopped it.”

It is extremely likely that a robust train control system would have prevented the accident, as it is capable of slowing the train sufficiently before it reaches a speed restriction. The bulk of this post will be dedicated to talking about what train control systems can do. There’s a large array of acronyms, some of which mean different things in different countries, and one of which has two different meanings.

Broadly speaking, train control can prevent two types of dangerous driving: crashing into another train on the same track, and excessive speeding. If the system detects dangerous behavior, it will automatically stop or slow down the train. Driverless trains are based on robust enough systems that are so automated they no longer need the driver. The hard part is having an on-board system figure out whether the train is traveling too close to another train or too fast, which requires communication with the signaling system; automatically slowing the train down is comparatively easy. In nearly all cases, the signals are static and embedded in the track systems, but in a few, usually high-frequency subways rather than mainline rail, the system directly communicates with the train ahead on the same track (this is moving block signaling, or communication-based train control).

It is century-old technology to stop a train that is about to enter a segment of track too close to another train (“signal passed at danger,” or SPAD). A train’s steel wheels close an electric circuit that detects whether there is a train on a block of track, and this communicates to the signals entering this block of track to prohibit trains from proceeding; see diagrams in the moving-block signaling link, which also show how it works in the more common fixed-block setup. A situation that electrically insulates the train from the track is therefore extremely dangerous and may lead to line shutdowns for safety. Any system with the capability to stop a train in such a situation is called automatic train stop, or ATS. The 79 mph speed limit on nearly all passenger train lines in the US comes from a 1947 regulation by the Interstate Commerce Commission (which has since morphed into the FRA) requiring ATS or in-cab signaling at higher speed; the intention was to force the railroads to install ATS by threatening a crippling speed limit, not to actually reduce train speed.

It is much harder to enforce speed limits. ATS systems do not have to enforce speed limits: at Amagasaki, there was an ATS system that would have stopped a train running a stop signal (as it had earlier on the trip), but no protection from excessive speeding, which is what led to the crash. The signaling system needs to be able to communicate both permanent and temporary speed restrictions. It is nontrivial to maintain an up-to-date database of all speed restrictions on an on-board computer, or alternatively communicate many different speeds from wayside track signals to the train’s computer.

In 2008, the FRA mandated positive train control (PTC) as a result of the Chatsworth crash; PTC is a term that doesn’t exist outside North America, and refers to an automatic train control system capable of not just ATS but also enforcement of all speed restrictions. In Europe it is called automatic train protection, or ATP, and in Japan it is called automatic train control, or ATC. It is common in the US to do trackwork on one track of a multiple-track railroad and slap a temporary speed restriction on adjacent track, and enforcing such limits to protect wayside workers is specifically part of PTC.

Because the ATC system requires trainside equipment, a train that travels between different systems will need more equipment, raising its cost. In Europe, with its hodgepodge of national standards, some international trains require 7 different systems, raising locomotive costs by up to 60%. This led to the development of a unified Europe-wide standard, European Train Control System (ETCS), which combined with GSM radio for communication between lineside signals and the train is called European Rail Traffic Management System (ERTMS). The obligatory cost and schedule overruns of any IT project have plagued this system, and led to delays in installing train protection on some lines, which led to a fatal accident in Belgium. However, the agony of the ERTMS project has for the most part already passed, and now there is a wide variety of vendors manufacturing equipment to the specified standards, leading to widespread installations on new and upgraded lines outside Europe. As of September of 2013, ETCS is installed on 68,000 track-km and 9,000 vehicles worldwide.

Although ETCS is an emerging global standard (outside Japan, which has a vast system of domestic ATC with multiple domestic vendors), American agencies forced to install PTC have not used it. California HSR is planning to use ETCS, and Amtrak’s signaling system on much of the Northeast Corridor, Advanced Civil Speed Enforcement System (ACSES), with full implementation on the Northeast Corridor expected by this year, is similar to ETCS but not the same. Elsewhere in the US, systems have been bespoke (e.g. on Caltrain), or based on the lower-capacity systems used by the freight operators.

Metro-North does not have PTC. It has an ATS system that protects against SPAD, but can only enforce one speed limit, the maximum speed on the line (MAS). As the maximum speed on the outer Hudson Line is 90 mph, the system cannot enforce any lower speed, and so the train could travel at 82 mph even in 70 or 75 mph territory, let alone 30 mph territory. More modern systems can enforce several speed limits (e.g. the TGV’s TVM), and the most modern can enforce any speed limit, in 1 km/h or 1 mph increments.

Metro-North and the LIRR have been trying to wrangle their way out of the PTC mandate, saying it offers “marginal benefits”; a year and a half ago, the New York Post used the word “outrageous” to describe the PTC mandate, saying it would cost over a billion dollars and that the money could go to capacity improvements instead, such as station parking. Lobbying on behalf of Metro-North and the LIRR, Senator Charles Schumer made sure to amend a proposed Senate transportation bill to give the railroads waivers until 2018, so that they could devote resources to more rush hour capacity from the outer suburbs (such as Ronkonkoma) to Manhattan and fewer to safety. According to Siemens, the work will actually take until 2019, and Siemens says it “has developed PTC specifically for the North American market,” in other words built a bespoke system instead of ETCS. (ACSES was developed by Alstom.)

Because the systems developed for the US are based on the needs of American freight railroads and perhaps Amtrak, which do not need as much capacity in terms of trains per hour as the busiest commuter lines, they are much lower-capacity than those used in Europe. The LIRR and Metro-North have far busier mainline tracks than any other US commuter rail system with the exception of the inner part of New Jersey Transit, which is equipped with ACSES as part of the Northeast Corridor; to modify the system to their needs raises costs, as per the New York Post article. The MTA released the following statement (see also mirrors on Fox and CBS):

The MTA began work to install Positive Train Control on the Long Island Rail Road and Metro-North Railroad in 2009. To date, the MTA has budgeted nearly $600 million for elements of PTC installation, including a $428 million procurement last month for a system integrator. Full implementation is estimated to cost $900 million, and the MTA will make sure the appropriate funding is made to implement PTC on the most aggressive schedule possible. However, implementing PTC by the 2015 deadline will be very difficult for the MTA as well as for other commuter railroads, as the Federal Railroad Administration (FRA) and the Government Accountability Office (GAO) have both concluded.  Much of the technology is still under development and is untested and unproven for commuter railroads the size and complexity of Metro-North and LIRR, and all of the radio spectrum necessary to operate PTC has not been made available. The MTA will continue its efforts to install PTC as quickly as possible, and will continue to make all prudent and necessary investments to keep its network safe.

Of course, the technology is no longer under development or untested. Just ask the Belgians, the Swiss, the Chinese, the Saudi, or the Taiwanese. Older technologies meeting the definition of PTC exist practically everywhere on mainline trains in the European and Asian first world. Urban commuter lines in Tokyo such as the Tokaido Main Line and the Yamanote Line, each with more ridership than all North American commuter lines combined, are equipped with ATC. The RER A, with slightly less ridership than all North American commuter lines combined, has a train control system providing moving-block signaling capability on the central trunk. A Swiss mainline with 242 passenger and freight trains per day and minimum train spacing of 110 seconds at 200 km/h has ERTMS as its only ATP system, and Switzerland expects to fully equip its network with ERTMS by 2017.

Although the US mainline rail system is freight-primary, with different needs from those of Europe south of Scandinavia (e.g. critical trunk lines are thousands of kilometers long and lie in sparsely-populated territory), the same can’t be said of the Northeastern commuter rail lines, most of which only see a few daily freight trains and are dominated by tidal flows of commuter trains with high traffic density at rush hour. Rush hour traffic levels approaching 20 tph per track are routine, with 24-26 on the Northeast Corridor entering Penn Station from New Jersey. It is incompetent to try to adapt a system developed for long-distance low-cost freight railroads and ignore one developed for busy commuter lines just because it has an E for European in its name.

While most European countries have long implementation timelines coming from a large installed base of good but not top-line legacy signaling, countries with inferior systems sometimes choose to replace their entire signaling systems, as the passenger-primary parts of the US should. Denmark, whose intercity rail far lags that of most peer European countries, decided to replace its signaling system entirely with ERTMS. The projected cost is €3.2 billion, of which €2 billion is for ERTMS on the network, €400 million is for equipping the Copenhagen S-Bahn with CBTC, and €800 million is contingency; the total length of the system is 2,132 route-km and 3,240 track-km.

At a million euros per route-km, exclusive of contingency, Metro-North could install the system on all east-of-Hudson lines, except the New Haven Line, where Amtrak plans to install ACSES, for about $450 million, and the LIRR could install the system on its entire system (including parts currently without any signaling) for about $650 million. Denmark has about 700 trainsets and locomotives to install the system on, in addition to tracks; on the LIRR and Metro-North, those figures are about 150 each, although this assumes that trainsets would be permanently coupled, whereas today they run in married pairs, so that in an eight-car unit there are four cabs where only two are needed. If the LIRR and Metro-North agreed to treat trains as permanently-coupled sets, then the scope of the order would be about 40% of the size of the Danish fleet, consistent with a total cost of about a billion dollars.

This would also allow higher capacity than the current systems, which could squeeze more trains onto busy lines, so it wouldn’t be at the expense of capacity improvements. In particular, the LIRR could keep postponing the $1.5 billion Main Line third track to Hicksville project, and instead run trains on the currently double-track bidirectionally (today they run one-way at rush hour, to accommodate local and express service) using the very high frequency that ETCS permits. Another project, which Sen. Schumer thinks is more important than PTC, a $400 million plan to double-tracking the outer part of the Main Line from Farmingdale to Ronkonkoma, could also be postponed while still providing the necessary capacity.

Although both of the LIRR multi-tracking projects’ cost figures are enormous – the third track is about $100 million per kilometer, almost what a subway in suburbia should cost, and the outer second track is $15 million per km, more reasonable but still very high – adding tracks is in general more expensive than adding signals. IT procurement is expensive and prone to cost overruns, but once the initial system has been developed, the marginal cost of implementing it in new but similar environments is relatively low; ETCS would cost about the same on the LIRR and Metro-North as the MTA plans to spend on signaling, but provides better functionality as it’s compatible with their high traffic density. Organisation vor Elektronik vor Beton.

Of course the first step in the organization before electronics before concrete slogan is improving the state of the organization. In terms of safety, there may be scope for better training, but the train driver according to the NTSB has 10 years’ experience (start at 02:20 in the video) and based on his work schedule would have had enough time to get a full night’s sleep before his shift started (start at 07:25). Since there is no obvious organizational way to further improve safety, electronics is the next step, and this means installing a good PTC system in a timely manner.

However, in terms of cost, there is something to be done. While the MTA claims PTC is too expensive and provides little benefit, Metro-North spent $80 million a year on conductors’ salaries in 2010 (although it’s been going down, to about $65 million by 2012) and the LIRR spent another $95 million (in either 2010 or 2012), both numbers coming from the Empire Center’s SeeThroughNY. About six years’ worth of conductor salaries would pay for full PTC; future savings are free. The NTSB briefing said there were 4 conductors on the train (start at 09:15). The main duty of conductors is to sell, check, and punch tickets, an old-time rail practice that has been abolished in modern commuter railroads throughout the first world.

A commuter train needs between 0 and 1 conductor. Stephen Smith quotes Vukan Vuchic, a professor of transportation engineering at Penn who was involved in the implementation of SEPTA’s through-running in the 1980s, as saying that ticket-punching is “extremely obsolete” and “very 19th century.” A tour of any of the major urban commuter rail systems of Europe will reveal that a few, such as the Paris RER and the London systems, use turnstile, while most use proof-of-payment, in which roving teams of ticket inspectors only check a small proportion of the trains, slapping fines on people caught without a valid ticket. On American light rail lines, which are often similar in role to German commuter rail lines (especially tram-trains) except that they run on dedicated greenfield tracks, this is routine; this can and should extend to commuter mainlines. While the electronics is needed to handle safety, this organizational improvement would pay for the electronics.

Although the investigation seems to be going in a competent manner, the MTA’s position on the relevant issues in general does not come from a position of competence. It is not competent to have this many redundant employees but then cry poverty when it comes to avoiding crashes and derailments. And it is not competent to pretend that there is nothing in Europe or Japan worth using for American signaling systems. The US did not invent PTC – at most, it invented the term for what’s called ATP or ATC elsewhere. It shouldn’t act like it’s the only place in the world that uses it.


  1. letsgola

    Thanks for the detailed summary of different technologies!

    Without wading into the debate on I-ETMS, ERTMS, ACSES, and unique systems like CBOSS and whatever MNR & LIRR are planning, we should at least note that the most egregious civil speed restrictions – like the curve in question – could be enforced by cab signals at a trivial cost.

    MNR’s existing cab signals have codes for 0 mph, 30 mph, 45 mph, and MAS. Typical practice in the US is to ignore civil speed restrictions, e.g. a 75 mph curve in territory otherwise good for 90 mph, since there’s no cab code available. But on a severe curve like this, they could pretty easily modify the cab signals to never give anything above 30 mph on the signal block containing the curve. (There’s a capacity impact, but that block is obviously bounded by the interlockings immediately north & south, so the capacity loss shouldn’t be that bad.)

    Depending on what’s out there (processor based or relay based), it’s either a change to software, or some wiring changes and cutovers in the signal houses… something they should be able to design in a matter of months and implement quickly, right?

    • Patrice

      Thanks for the timely post, Alon. Can you comment on the feasibility of straightening that curve? It is a rather notorious one which caused a costly trash train derailment this summer which took several days to fix. A NY Times article this summer mentioned that there have been other problems with this stretch of track. While PTC could make it safer, what about adjusting the tracks to make them straighter or more elevated? It seems like everyone on the Hudson Line is at the continual mercy of sleepy speeding engineers for the next several years. Thanks.

      • Alon Levy

        The tracks wrap around a hill. The Hudson Line isn’t easy to straighten; the curves whose inside points west rather than easy are actually easier, since it’s easier to fill shallow water than to cut steep hills. The hill at Spuyten Duyvil specifically rises directly from the inside of the curve: see photos here and here (search under “from the air”).

        Now, it’s possible to squeeze much more speed from this curve than the current limit. With vanilla superelevation of 75 mm and 150 mm cant deficiency (not allowed under current FRA regulations but a revision is about to make this possible with some testing for passenger comfort), ~65 km/h is possible. With full superelevation of 150 mm, which isn’t compatible with (minimal) freight traffic on the line as currently practiced, make it 77. 132 km/h, or 82 mph if you will, is far beyond what any train could safely do on this curve.

        • Nathanael

          Not sure you can actually superelevate that curve much — remember, it curves right into a switch, which can’t be superelevated easily.

          • Adirondacker12800

            Move the switch. Theres always going to be freight moving through there so at least one of the tracks needs to be able to carry freight.

          • johndmuller

            There’s a lot happening there in a small section of track. In general, the 4 track Hudson line is 3 tracks in the midst of becoming 2 tracks in order to negotiate a 2 track cut through a rock outcropping. Immediately to the south of the derailment is a station whose platforms could easily have involved in the crash if the train had stayed on or closer to the rails longer. Immediately north is the turnoff for the ‘Empire Connection’ (west side of Manhattan to Penn) and its turnout switch; also a number of other turnouts to enable trains to adjust tracks and/or make that turnoff. Going south there is the merge to two tracks, that rock cut, some more curvy track and another station before another fairly sharp turn to get back onto another reasonably straight shot south.

            Basically there is a fairly abrupt jog to the east between the straight sections – it’s a section that just needs to be taken slowly, no real point in messing with it (although the leftover rock outcropping between the track and the water seems like it should/could come down – it’s quite high and only about 15-20 feet thick – not much to gain doing that though unless one could add another track all the way through there).

          • Richard Mlynarik

            As an aside, there’s no rail-technical, geometrical, safety, or maintenance reason not to place turnouts on superelevated curves.


            Or do an image search for “Überhöhung bogenweiche” or the equivalent in other languages (“superelevated turnout” yields much less, and mostly model train stuff.)

            It’s a matter of culture (US commuter rail standards being essentially being based around space-is-no-problem cheapness-is-all AREMA freight RR standards for corn silo sidings in Nebraska), not physics.

            Everybody’s standards prefer standardized geometry turnouts placed in straight and level locations, but outside North America you’ll find tens of thousands of routine exceptions. (Yes, there are exceptions here, but the engineering departments fight hard against them, often at the expense of capacity and capital cost, those being Somebody Else’s Problem and Not Part of the Design Standards Manual.)

          • Nathanael

            Richard, while your point is correct in general, in this case Amtrak (the express service) is taking the *straight* route, while Metro-North (the local service) is taking the *curved* route. Superelevating by any significant amount through the switch makes no sense — you don’t really want to tilt the express service onto its side while it goes straight ahead, which would be the result of superelevation.

            Superelevating in a turnout requires a tradeoff between the superelevation of the two routes, which means in this case that you can’t sensibly superelevate the curve.

            Frankly, this location (at the bottom of a cliff in a rock cut next to a river around a sharp turn) is a bad place to put a railroad, and there’s not much to be done about it.

            Restoring the upper Harlem Line for intercity service and building “Alternative G” from Grand Central to Penn Station for through service is probably the sanest thing to do, but that would cost money.

          • Joey

            Turnouts are not an issue for this particular curve. The empire connection switch (and all other switches) are nearly 300m north of the curve. The merge on the south side is past the station. The station itself is a constraint. As is the fact that freight needs to run through there occasionally, though the relatively high volume of passenger traffic should dictate the needs of the corridor more than the low volume of freight.

        • robertwightman

          Alon Levy says:
          “Now, it’s possible to squeeze much more speed from this curve than the current limit. With vanilla super elevation of 75 mm and 150 mm cant deficiency (not allowed under current FRA regulations but a revision is about to make this possible with some testing for passenger comfort), ~65 km/h is possible. With full super elevation of 150 mm, which isn’t compatible with (minimal) freight traffic on the line as currently practiced, make it 77. 132 km/h, or 82 mph if you will, is far beyond what any train could safely do on this curve.”

          I don’t know what conversion factors you are using but 77km/h is nowhere near 82 mph. It is just under 50 mph and 82 mph is about 130 mph. I appreciate your use of metric units and ISO dates but please get the conversions correct.

          The TTC uses timing signals in areas with speed restrictions to enforce compliance with speed restrictions. The signal show red with a lunar white aspect underneath. If you obey the speed restriction you will get a green or yellow at the next signal before you reach it. If you ignore it you will get an emergency brake application. I don’t know if this is allowed under FRA rules but it works under 1950s transit signals.

  2. Tom West

    One of my concerns on seeing the accident site was the number of coaches that had overturned. One of the most effective ways to reduce passenger deaths (and injuries) in a derailment is to ensure coaches remain upright – which easiest if they remain coupled together.

  3. Don

    Really like the blog! A couple of thoughts.

    The “off the shelf” European system wasn’t quite ready for prime time when the PTC law was passed in 2008. The US RRs had to pick a path and stick to it at the start given the tight timeline. Given their level of comfort with previous ATCS trials and development work, PTC was the natural way to go. Further, they chose a vendor-specific solution in order to have a shot at the tight timeline rather than open-architecture which would have required considerably more inter-operability testing.

    Second, a good chunk of the US rail network that is required to have PTC currently has no signalling at all. There is little or no “dark” territory in Europe. A single PTC solution is needed for all territory.

    Third, commuter roads COULD have chosen a different system from the freight roads, but every nearly every one is a tenant on a freight road for part of their operation. (The LIRR might be the single exception – but they need ACSES compatibility to get into Penn Station over Amtrak). Similarly, the freight roads are tenants on commuter roads, as well. Maintaining dual equipped locomotive fleets and/or segregating their assignments is a non-trival problem. In fact, having ACSES compatible PTC in order to operate over Amtrak in the NEC is a major issue for NS.

    Finally, I believe that Amtrak’s ACSES is the brain-child of Amtrak’s C&S department, particularly one signal engineer, Larry Light. It is really just PRR cab signalling with a second layer of carrier plus a transponder/antenna system for civil speeds. It’s a hot mess IMHO….but I’m a Mechanical Engr, so what do I know?

    • Alon Levy


      Re your thoughts:

      1. The domestic systems weren’t quite ready, either. ITCS had some embarrassing IT-related problems. The systems that were ready, like D-ATC, were and still are ignored. I’m also puzzled as to why vendor-specific solutions would meet tighter deadlines – vendor lock tends to make it harder to switch away when there are problems; and besides, entire national systems are planned to finish ERTMS installation before the LIRR and Metro-North plan to finish installing PTC.

      2. ERTMS Level 2 would be perfect for such a situation. In fact the reason why you see relatively slow adoption in France and Germany is precisely that they have tons of legacy signaling. The US to a good approximation has none. It’s similar to platform heights: Continental Europe, with its huge installed base of 550- and 760-mm platforms, is buying low-floor trains, but the US, which has no usable platform height in service lower than 1,220 mm, instead raises platforms from near-zero to full height when modernizing lines. Now, it’s true that the US has remotely located main lines, whereas the costs of ERTMS are designed around the needs of denser areas, but Scandinavia also has remote main lines, and there’s a version of ETCS whose name escapes me that is designed to require less infrastructure to suit Scandinavia’s needs.

      3. We’re not talking about New Mexico Rail Runner here; we’re talking about railroads without much freight traffic, and a lot of passenger traffic. Caltrain, a railroad that sees a couple of money-losing freight trains per day, is designing a bespoke PTC system even though it’s about to be hosting a high-speed rail system whose specs made it obvious from day one that it was going to use ERTMS Level 2. Metro-North isn’t anyone’s tenant east of the Hudson (and west of the Hudson it’s NJT except funded by New York State) and although it and the LIRR are saying they’re installing a system based on ACSES, they’re not actually installing ACSES.

      4. I’ve heard a bunch of different things about ACSES. At the other hand I’ve heard it’s a lot like ETCS Level 1, although that might just be the vendor.

    • Adirondacker12800

      The freights and Amtrak et al. have confirmed interoperability, from multiple vendors between ETMS or ITMS or whatever the freights are calling it this week and ACSES. There’s enough of a market between the commuter railroads and Amtrak to attract multiple vendors providing equipment at competitive prices and North American freight will have one of the biggest markets worldwide. Yes ERTMS will be deployed more widely but with a tweak for Obscurastan that makes it incompatible with everything else which is different from the tweak in Freedonia which is different, all of which are incompatible with the subset that China is using. Everything in North America will be converging on one single standard because a freight locomotive in California can end up in Maine and one in Florida can end up Washington state. and they all can occasionally wander off to Mexico or Canada. And someday far far in the future when Metra needs something better than what the freights are using they are gonna go with whatever the commuter agencies in the Northeast are using because theres a large market with competitive prices and all the North American tweaks have already been done. And the Amtrak trains that share Union Station are already equipped.

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  5. Adirondacker12800

    The 79 mph speed limit on nearly all passenger train lines in the US comes from a 1947 regulation by the Interstate Commerce Commission (which has since morphed into the FRA) requiring ATS or in-cab signaling at higher speed; the intention was to force the railroads to install ATS by threatening a crippling speed limit, not to actually reduce train speed.

    The intention was to stop trains from crashing into each other.

    79 mile per hour maximum speed for lineside signals is rational.
    I don’t have the time or patience to go find sources, though I think the guy who runs the Pedestrian Observations blog observed this, worldwide the requirement for signals more sophisticated than lineside signals clusters around 80 milles per hour 125/130 kilometers per hour. It’s the limit of a human’s ability to see the signals in time to stop the train before it crashes into something ahead.

    • Alon Levy

      Actually, no, the limit of lineside signals in Europe is closer to 160-200 km/h (160 in Germany, 125 mph in the UK). In contrast, the US has a higher nominal speed limit for grade crossings – 125 mph in principle, although 110 mph in practice – than the many European countries where the limit is 160 km/h (or Japan, where if I remember correctly it’s 130 km/h de facto).

      The ICC intended to make trains stop crashing, yes, but it had been badgering railroads about installing ATS since 1922. The intention was to improve safety by getting railroads to install ATS, not by getting them to slow down. This is probably why it specified limits in terms of maximum speed and not maximum braking distance (which was the proximate cause of the Naperville crash): the intention was to harass railroads into installing ATS.

        • Max Wyss

          Stopping the train fat enough by the time he sees the signal… That’s not working anyways, and essentially all signals have an announcement signal (stating “the next/main signal has this aspect). It is common understanding in Europe (Germany, France, Switzerland) that the maximum speed for a signal to be recognizable for a sufficiently long time, even under adverse weather conditions, is 160 km/h; above that speed, cab signalling is mandatory. How the information goes from the lineside devices to the cab equipment does not need to be specified.

          Most systems work with fixed locations (when it comes to transmit the signal aspect at the signal’s place); ETCS L1 LS (that’s “limited supervision”) is an example for that, as well as ZUB, KVB, etc.). If brake curves (with distance dependent maximum speed) is required, a linear system is necessary. Such systems have a radiating cable between the rails, which repeats the aspect of the main signal (or the valid signal). Based on that, the distance from the “point of danger”, and the braking curve of the train, the on board computer can calculate the maximum speed, and apply brakes if needed. Germany uses such a system extensively (LZB, “Linienzugbeeinflussung”). But ETCS L1 LS can be extended with loops as well.

          So, in order to protect a sharp curve, a linear system is necessary.

          Central supervision is not really feasible, except in some well limited and controlled environments (such as subways); It is the train which has to do its own calculations, based on its current location and the distances from the point of danger.

          • Max Wyss

            aargh, Note to self, proofread posts before hitting the post comment button.

            The first sentence should begin with “stopping the train fast enough…”

          • Andrew in Ezo

            Likewise in Japan the limit for lineside signals is 160km/h. Above that requires cab signals. On the Keisei Sky Access route to Narita Airport, there is a stretch of line with 160km/h running- it equipped with 6 lamp lineside signals, which allow a double green indication which replaces an announcement signal (in general signal spacing is closer in Japan than in Europe).

  6. Alex B.

    From the Times:

    The Metro-North Railroad train that derailed on Sunday included a system designed to warn an operator of a potential accident. But such an “alerter,” which can automatically apply the brakes if an operator is unresponsive, was not in the cab where William Rockefeller apparently fell into an early-morning daze at the controls. It was at the other end of the train.


    And then there’s this:

    In an interview with a radio station on Wednesday, Gov. Andrew M. Cuomo called positive train control “somewhat controversial,” adding that some people “say they’re not everything they’re cracked up to be.”

    The authority said earlier in the week that the technology remained “untested and unproven for commuter railroads the size and complexity” of Metro-North and the Long Island Rail Road. Mr. Lisberg added that the authority remained committed to installing the system as soon as possible, saying that “money is not an obstacle.”

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  8. Robert Levine

    This seems like a ridiculously easy problem to fix. An onboard GPS-based system (with some software for “coasting” in the absence of GPS signals), working on a database of maximum speeds per track segment. Database updated nightly via wifi or cellphone. Output would be a visual cue in the cab, coupled with the equivalent of a stall horn in an aircraft.

    • Alon Levy

      GPS doesn’t actually work. It’s not precise enough or reliable enough. Its precision is to within a few meters, more than the track centers on double track, so the system wouldn’t be able to figure out which track the train is on. It also doesn’t work in cloudy weather.

      It’s not actually easy to install electronics, especially on systems with a huge legacy installed base (i.e. not the US, where preexisting signaling is primitive enough that it can be scrapped with the possible exception of ACSES). It involved years of agony and fatal accidents in Europe to get it right. It’s just that it’s working now, after all the bugs have been worked out.

      • Adirondacker12800

        GPS definitely wouldn’t work in tunnels. So you have to have a whole full blown signal system on board the train that can navigate Grand Central or Penn Station. It would have the same problem in Newark, 30th Street, Jamaica, probably Trenton and few other bigger stations like New Haven. South Station? Providence? It’s cheaper and easier to just go with one.

        • Patrick @ The LIRR Today

          And considering some trains literally operate within feet of each other on the LIRR at terminals like Jamaica and Huntington. PTC as it is now will probably be jumpy enough, and just imagine how troublesome it could be if everything had to be spotted from space. (but since PTC will not be installed in terminal areas, hopefully it won’t be too bad).

          • Alon Levy

            (But the only terminal area that’s already PTC-ified is Penn Station – doesn’t the mandate cover everything else, including Grand Central and such?)

          • Adirondacker12800

            If you believe everything you read on Grand Central has a ten mile an hour speed limit and the conductor has to be in the cab.

      • asdfsdf

        Well, military grade GPS and differential GPS is actually accurate to within centimeters, and you could probably use computers to figure out the rest when outside of a station. However, if the cost is due to track infrastructure and in-car infrastructure, and if you need to have track infrastructure to communicate anyway, it’s not clear that GPS would save you much money, and it would be more vulnerable to interference and tampering.

    • Nathanael

      The attempt to use GPS rather than tried-and-true track circuits is what caused the US railroads to waste a fortune without building a working system.

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