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JR test self-driving Shinkansen


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https://www3.nhk.or.jp/nhkworld/en/news/ataglance/1816/

 

Few details, maybe someone can add a more detailed article from a Japanese newspaper.

 

This makes sense I suppose, especially with the new linear shinkansen. It's already so fast that signals are impossible to see and everything is communicated electronically, and the drivers famously are required to follow the manual precisely and not try to memorise or improvise anything.

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It's a logical move. The Shinkansen lines would be comparatively easy to fully automatize since the they are segregated from the legacy network. It would be a lot harder to achieve with the TGV or the ICE.

 

Other sources:

https://www.asahi.com/ajw/articles/14483444

https://www.railjournal.com/signalling/jr-east-to-trial-ato-and-5g-on-joetsu-shinkansen/

https://www.jrailpass.com/blog/driverless-shinkansen
 

Quote

The trials will take place in October and November 2021 using an out–of–service 12-car train on the 5km stretch between Niigata station and the Niigata Shinkansen vehicle depot. The ATO trials will consist of remote departure, tests of the ATO system to automatically accelerate and decelerate the train, automatic stopping in a pre-determined location, and emergency stop procedures.


[...]

 JR East says experience from these trials will support the wider deployment of ATO across its Shinkansen network, a policy included in the railway’s Transformation 2027 strategy.

Edited by disturbman
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TokyoImperialPalace

I wonder how the system would react to something bizarre like people climbing out of windows, or even smashing a window and climbing out? I can envisage a situation where the train tries to correct itself with the platform doors while passengers and half-way out of the windows.

 

Though generally I am supportive of automation, with possibly a train engineer (similar to the old flight engineers that airplanes used to have) for safety reasons. I would also retain at least two staff who are trained in operating the train and safety features, albeit one of them could act as a conductor.

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8 hours ago, disturbman said:

It's a logical move. The Shinkansen lines would be comparatively easy to fully automatize since the they are segregated from the legacy network. It would be a lot harder to achieve with the TGV or the ICE.

 

I totally agree. That's one of the major advantage of having a dedicated network when you want to automate it. If you make a comparison with Paris'metro, line 14 was designed as automated line whereas line 1 was turned into an automated line.  The automation itself was not the most complicated part of the project compared to the changes to adapt the plaforms (esp. for those curvy). They didn't tried to 'update' the old metro, they simply changed it. 

 

4 hours ago, TokyoImperialPalace said:

I wonder how the system would react to something bizarre like people climbing out of windows, or even smashing a window and climbing out? I can envisage a situation where the train tries to correct itself with the platform doors while passengers and half-way out of the windows.

 

 

You're in Japan, not in Russia. Moreover, there are plenty of JR people in and out of the train. 

 

 

4 hours ago, TokyoImperialPalace said:

Though generally I am supportive of automation, with possibly a train engineer (similar to the old flight engineers that airplanes used to have) for safety reasons. I would also retain at least two staff who are trained in operating the train and safety features, albeit one of them could act as a conductor.

 

Remote control of a train is probably far easier and more efficient. One global control room, a couple a well experimented people, a pinch of computers and you fix it. If it doesnt work, it's probably more serious and then it's not an issue the 'spare' driver can fix. My son is train driver and explained me he was obliged to use a cellphone to contact the support unit when he has a technical issue that affected also the inner radio network. Quite funny (after having crushed a family of wild pigs)

 

JM

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2 hours ago, JR East said:

They didn't tried to 'update' the old metro, they simply changed it. 


The difference between transformation and transition. In my perspective, it was just an update to modern standards, the subway was already operating at level two automation since the late 60s with the tapis de pilotage automatique.

 

6 hours ago, TokyoImperialPalace said:

Though generally I am supportive of automation, with possibly a train engineer (similar to the old flight engineers that airplanes used to have) for safety reasons. I would also retain at least two staff who are trained in operating the train and safety features, albeit one of them could act as a conductor.


I think you are a bit too conservative. Fully automatic subway trains have been running without staff onboard since the early 80s (Lille VAL). At our technological level, there is no need for onboard operators anymore. But I can understand the psychological need of having boots on the ground to reassure passengers, it would in any way make sense for long distance trains and help in case of evacuations/emergency.

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trainsforever8
12 hours ago, disturbman said:

It's a logical move. The Shinkansen lines would be comparatively easy to fully automatize since the they are segregated from the legacy network. It would be a lot harder to achieve with the TGV or the ICE.

 

Other sources:

https://www.asahi.com/ajw/articles/14483444

https://www.railjournal.com/signalling/jr-east-to-trial-ato-and-5g-on-joetsu-shinkansen/

https://www.jrailpass.com/blog/driverless-shinkansen
 

Do we have more information about that "transformation 2027 strategy"? I'm interested in seeing what they are planning to realize.

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I think some people may not realise, that part of the actual driving is already being performed automatically at this moment, and how this has been the case since the very beginning. It is also important to note, that the shinkansen has been using a cab signaling system ever since the beginning, ATC-1A, which was closer to a semi-ATO system than some may realise. Though there were a limited number of signals and signs, mainly in yards, and while there used to be a limited number of signed speed limits on the Tōkaidō Shinkansen between Tōkyō and just after Shinagawa, and on the Tōhoku shinkansen in the tunnel to and from Ueno, all of the regular signaling is done via the ATC systems, though the current digital systems are more advanced the basic operational principles haven't really changed all that much since 1964.

 

While I could've finished my response at this point, it wouldn't be one of my posts if I didn't use (abuse?) the above as a lead in for some additional content about the (early) ATC systems, and their development into the systems in use today, now would it😅.

 

 

Anyway, to provide a broader picture into the development of the ATC (automatic train control) systems for the shinkansen, I think it would be best to look into the first ATC system developed for the Tōkaidō Shinkansen, ATC-1A.

 

Though the shinkansen has become, perhaps one of the most potent symbols of Japanese technological prowess and cutting edge technology, in the west, it may come as a surprise that the technology developed for the Tōkaidō Shinkansen, and for what would later become the 0 series, was never intended as such.

The core group working on the shinkansen project would set themselves the goal of creating the safest and most reliable railway system possible, which wasn't really that strange considering the intense skepticism, surrounding the project at that point in time, from both a majority inside J.N.R. and the diet.

 

As such the ATC system developed for the shinkansen had to be 1) be able to stop the train, even if one of the systems failed (fail-safe) 2) had to have enough redundancies to ensure a high degree of safety 3) It had to be able to send a signal to the train, even if the train was stopped. i.e. no line side beacons, the signal had to be constantly receivable at all moments 4) the electric circuit had to be simple 5) rather than just providing speed control, it also had to be able to control the deceleration of the train.

 

The resulting ATC-1A system, as introduced on the Tōkaidō Shinkansen, would fulfill all 5 of the stated criteria, which included automatic braking (ATC brake) and speed monitoring (slowing the train down if above the ATC limit).

ATC-1A/B/S would be a track based system,  it would be using a single channel signal current, which was to be transmitted through the track, with different frequencies corresponding to different signals.

Insulated sections every 1,5 km allowed for the shinkansen to be divided into block sections, with a single block occupying two such sections, which gave a block length of 3km. Electric coils, with a number located in every section, would be used to energise the track at the correct frequency matching the required ATC limit.

On the car side, a so called speed generator, a small electric generator (nothing more complex than a electromagnetic coil) was attached to the gearbox (on the driving shaft end), with a current being generated every time a tooth passed the coil generating an electric current at a certain frequency, the higher the speed the higher the frequency. By calculating the different frequencies corresponding to the different speeds it allowed the system to check if the frequency matched with the current ATC limit. Three independent speed control units would receive this current, and translate it into brake commands, or release commands when necessary.

 

ATC-1A would be used on the Tōkaidō Shinkansen, while the section between Shin-Ōsaka and Okayama, opened on March 15th 1972, would be using ATC-1B, while the section between Okayama, opened on March the 10th 1975, would be using ATC-1S. Though there were some minor differences between those systems, they did function in a similar manner.

 

ATC-1A, and all later versions, worked with a speed check system, if the shinkansen was traveling at speed which was higher than the ATC speed limit, the brakes would be applied automatically (combined braking (rheostatic (dynamic) braking + additional air brakes when needed) above 50km/h (changed to 30km/h and up with the introduction of the 22nd batch of the 0 series, the 1000 sub-type cars introduced in the second half of 1976. The 200 series was the first to have combined braking all the way till stopped) and air braking when below 50 (30) Km/h) and are also released automatically when below the ATC limit, with the exception of the ATC 30 signal which has to be manually confirmed, when the train has decelerated to 30km/h or lower, before the brakes release (failure to confirm will lead to the bakes not releasing, a safety feature should the driver be incapacitated). Deceleration rates where, and still are, regulated depending on the speed range, from 160km/h and up it was limited to 1.4 km/h/s (kilometres an hour per second)(2.0 km/h/s under emergency braking), between 160 to 110 it was 1.84 km/h/s (2.64) and between 110 and 0 it would be 2.50 km/h/s (3.54). This was done as a safeguard, preventing the wheels from locking up at higher speeds, which could lead to derailments in a worst case scenario (not to mention degraded braking performance).

 

With ATC-1A  the following ATC limits could be enforced: 0 (stop, there were 3 signal frequencies which could lead to a stop signal, but let's leave it at just 0 for this time) - 30 -70 - 110 - 160 and 210. This meant that on a regular approach to a stop, the ATC signal would first drop down from 210 to 160 down to 110 then to 70, and more or less at the beginning of the platform an ATC beacon would drop the section limit down to 30 km/h after which the driver would take over and stop the train at the correct position, if he didn't there was an ATC beacon prior to the end of the platform which would transmit the ATC-0 signal which would stop the train before it could enter the active line.

However, as the technology wasn't quite there yet, in practice the initial braking application by the ATC came on quite harshly, which led to a decrease in passenger comfort. As such, prior to the 1980's, shinkansen drivers would be slowing down to the ATC limit prior to the ATC signal changing, which though it resulted in a more comfortable passenger experience, was also quite inefficient as shinkansen trains would slow down much earlier than strictly necessary. For example, on a station approach the driver would decelerate from ~200 to 160 well before the 160 signal would be received, with the same happening before the 110 signal the 70 signal etc. As a result the shinkansen would slow down about a block section (3 km) earlier than it would otherwise do so if under ATC braking, this type of driving resulted in longer travel times, and even though this was accounted for in the timetable, it was of course not the most efficient time wise, and ran counter to the original idea behind the design of the ATC-1 system.

 

 

This would change after the introduction of ATC-1D in 1982. ATC-1D, which was first introduced with the opening of the first section of the Tōhoku Shinkansen on the 23rd of June 1982, was designed for use on the nationwide shinkansen network, so for both the 60Hz (Tōkaidō/Sanyō Shinkansen) and 50Hz (Tōhoku and Jōetsu) shinkansen. Though officially referred to as ATC-1D, the receiving system onboard the Tōhoku and Jōetsu Shinkansen trains, the 200 series, would be categorised as ATC-2. ATC-1D and ATC-2 would be dual channel systems, which means that they were operating on two sets of frequencies, as opposed to the single channel used for ATC-1A/B/S. This allowed for more steps to be added to the system, while at the same time the ATC brake application behaviour would be smoothed on the vehicle side as well. This resulted in ATC braking becoming the norm in regular operations, on these two shinkansen, from the very beginning.

 

The speed steps for ATC-2 (as per march 1985, prior to this 210 was the highest ATC limit) would be: 240 (+5) - 210 -160 -110 -70 -30 - 0

 

 

After the opening of the Tōhoku and Jōetsu Shinkansen, work started on introducing ATC-1D to the Tōkaidō and Sanyō Shinkansen, which was completed somewhere around the mid 1980's. The version on the Tōkaidō Shinkansen would bear the original designation, ATC-1D while the Sanyō Shinkansen would receive the, almost identical, ATC-1W (West), though a couple of years later, in 1992. Though unrelated, this came around the same time the maximum operating speed for both the Tōkaidō and Sanyō Shinkansen were increased for the first time, with the maximum operating speed being increased from 210km/h to 220km/h, with the timetable revision of the 11th of January 1986 for the Sanyō Shinkansen, and the 1st of November 1986 for the Tōkaidō Shinkansen. While the increased maximum speed wouldn't come with any additional  ATC limits, the onboard ATC equipment would be modified to receive, and display the new speed limits (110 was changed to 120, 160 became 170, and 210 became 220), while also compatibility with the upcoming dual channel ATC frequencies and ATC behaviour was improved (for example, the 210 ATC limit prior to this was an absolute limit, i.e., once the train reached 211km/h the brakes would be applied. After the modifications, a +5 speed margin was added to the 220 limit, which meant ATC would only apply the brakes if the train exceeded 225km/h), which included smoother ATC braking behaviour. This would result in ATC braking becoming the norm on the Tōkaidō and Sanyō Shinkansen from that point onward.

 

The ATC limits starting from November 1st 1986 would be:  220 (+5) - 170 - 120 -70 -30 - 0

 

After the J.N.R. split in 1987, modifications to the ATC-1/2 systems would continue. While still functioning under ATC-1S, the introduction of the 100 series V formations in March 1989, would see them fitted with modified transponders reading the ATC 220 signal as 230 (with corresponding max speed (+5)) while under ATC-1S (220 under ATC-1D). While the introduction of the 300 series in March 1992 saw the introduction of ATC-1W (ATC-1D) on the Sanyō Shinkansen (otherwise the 300 series wouldn't have been able to go beyond 220 km/h on the Sanyō Shinkansen), as well as the introduction of a number of new ATC signals to the ATC-1D/W system, with 230, 255 and 270 (+5) now possible. prior to the introduction the 500 series, in march of 1997, 275, 285 and 300 (+3) were added to the ATC-1W signals. For ATC-2, The 200 series F90 sub formations (F90~F93) formed in 1990, would have their ATC transponders, on the 222 type cars only (descending side) modified to read the 240 signal as 275 (+/-0), while the 6 H formations, formed between April and July 1990, would have their transponders (on both the 221 and 222 type cars) modified to read 245 instead of 240. While the introduction of the E2 series (J formations, March 1997, N formations, October 1997) and the E3 series (march 1997) would see ATC signals of 260 (Nagano/Hokuriku Shinkansen) and 275 (Tōhoku Shinkansen) being added.

 

The introduction of digital ATC systems in the 2000's by both JR East (2005) and JR Tōkai (2006) would see the end of the fixed block based, analog ATC systems. JR East would be introducing DS-ATC (Digital Shinkansen ATC) between 2002 and 2005 on both the Tōhoku and Jōetsu Shinkansen, while the Hokuriku Shinkansen would retain ATC-2 until 2013. Rather than using fixed block sections, DS-ATC works with a preloaded route database which it uses to continuously determine the ideal braking curve with regards to station stops and preceding trains/signals. Though it still uses similar ATC speed limit signals (though more flexible, and with more having been added since the introduction of the E5 series in 2011), being digital it can space those ATC limits much closer together allowing for a much smoother braking curve in comparison to the older analog systems which were bound to fixed sections they could control.

JR Tōkai would be introducing their own digital ATC system in 2006, ATC-NS (ATC New (system for) Shinkansen) works according to the same principles as DS-ATC, though instead of using a preloaded database, it continuously analyses the route ahead, using this data to determine braking curves etc. The Sanyō Shinkansen would be converted to ATC-NS in 2017, which would also be the end of ATC-1.

In terms of ATC braking both DS-ATC and ATC-NS would be improving on the older systems, though automatic (ATC) braking still remains the standard. One change that was made for DS-ATC though, and not for ATC-NS was the ATC acknowledgement speed, which has been set at 75km/h for DS-ATC while ATC-NS retains the 30km/h limit.

 

 

 

So, coming back to the topic at hand, taking into account that the shinkansen had been operated in a semi ATO state since the very beginning, I've always been wondering if and when it would be taken to the next logical step. Though I'm personally not a big fan of automation for automation's sake, I'm actually neutral on the whole ATO thing in Japan. First of all I understand the issues forcing them (sorta) onto this track (pun kinda intended), but most importantly I think ATO is kinda misunderstood in most cases, at least the current implementation of it in Japan. ATO doesn't necessarily mean driverless, in fact most Japanese ATO systems in operation at this moment still have a driver at hand. Conducterless would probably be a more apt description, as the driver has basically taken over the tasks normally performed by the conductor while the train is under ATO operation, while they are still required to drive manually on a regular basis, in order to maintain their skills. As such, when ATO will inevitably be implemented on the shinkansen, I'd expect there to still be a driver at hand, even though their function may be slightly different compared to what it used to be in the past.

 

Also, the focus on safety I've mentioned earlier is something that has been the centre pillar on which the shinkansen system has been build and operated over the past 57 years. And even though there has been a number of incidents over the year, this central theme does still remain an intangible part of the shinkansen. Which is why I expect to see this project keep to the same principles.

Edited by 200系
dyslexia...
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10 hours ago, 200系 said:

Though I'm personally not a big fan of automation for automation's sake, I'm actually neutral on the whole ATO thing in Japan. First of all I understand the issues forcing them (sorta) onto this track (pun kinda intended), but most importantly I think ATO is kinda misunderstood in most cases, at least the current implementation of it in Japan. ATO doesn't necessarily mean driverless, in fact most Japanese ATO systems in operation at this moment still have a driver at hand. Conducterless would probably be a more apt description, as the driver has basically taken over the tasks normally performed by the conductor while the train is under ATO operation, while they are still required to drive manually on a regular basis, in order to maintain their skills. As such, when ATO will inevitably be implemented on the shinkansen, I'd expect there to still be a driver at hand, even though their function may be slightly different compared to what it used to be in the past.


What you are describing as "conductorless", the semi-automated operations described as GoA 2, is how most automated systems were initially designed for security and technological reasons. This is what the tapis de pilotage automatique I described earlier was, a fully automated trains with drivers in charge of operating doors and driving manually on a regular basis in order to maintain their skills.

 

We are at point in technological development that would allow for the Shinkansen system to be moved to driverless automated operations (GaO 3) or unattended train operations (GoA 4). Due to system resilience, the driver could disappear in favor of an expended conductor role, who would also be trained to drive the train at speeds allowing for visual driving in case of a dysfunction. This is somewhat what exists on Paris line 14 since the operations began in 1998, the management team is trained to manually drive the trains in case of a system issue. On the original MP89CAs, there were hidden consoles at the cab ends. I do not know if this system has been retained for the automation of line 1 and line 4.

The next development will probably be autonomous AI-driven trains on legacy networks.

Edited by disturbman
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I'm reminded of a documentary I saw on NHK where a train departed 15 seconds late and the driver made it up with slightly faster acceleration. In the end he arrived at every station on the route within 1 second of the advertised time.

 

He also very carefully controlled the speed so that as the track speed limit fell the train decelerated to be just under it every time, giving the passengers an extremely smooth ride.

 

It will be interesting to see if the automated system can do stuff like that.

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It will do it if the system is programed for it. In all honesty, 15 seconds does not seem to be that difficult to make up. Sander will probably know more, but I expect the schedule is made in a way that allows trains to make up for a few minutes of delays if weather and traffic conditions allow.


I had a somewhat similar experience in a TGV. My train departed 20ish minutes late (iirc, it's been 20 years, my memory is a bit fuzzy) but managed to arrive at destination slightly earlier than as per the time schedule. The driver had specially maintained higher speeds to avoid some nasty freezing fog that was planned to set on a portion of the route. All trains after ours were delayed by half an hour or more.

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13 hours ago, disturbman said:


The difference between transformation and transition. In my perspective, it was just an update to modern standards, the subway was already operating at level two automation since the late 60s with the tapis de pilotage automatique.

 

I was not aware of this 'tapis de pilotage automatique' despite the father of a friend of mine was driver on line 1. Thanks for the information. 

 

What I know is the former MP59 have been deeply refurbished in the 90's - for few of them - in Fontenay-sous-Bois facilities (I was living 200 m away from there, frequently going there for visiting) the major part of them have been sent by to other facilities / refurbishement workshops in France

 

All the car sent by truck are loaded on the ramp with the exit to the street (sorry for the poor quality of the picture, I didn't had time to restore those paper print scans)

 

123015886_1981_09.RATP06(2).thumb.jpg.52bd28b8c81f071d1d49f60fdb0ac1f5.jpg

 

Anyway, if I'm not wrong, the change from MP59 to MP89 was prior to the automation of line 1 and now there are only MP05 without cabin. 

 

As you can see, the date is 1981, at that time, the old Sprague-Thompson metros were sent for scrapping by rail to the scrapping plant (RATP - Ramp to FSB freight Station - Connecting to RER A - SNCF network somwhere arond Sucy-Bonneuil - Scrapping plant)

 

2037217434_1981_09.RATP07(2).thumb.jpg.b1ed165cd1d7a33dcea77159c66a02b7.jpg

 

983873351_1981_09.RATP08(2).thumb.jpg.4d5535197ec7b2ce20503a8b97e650fe.jpg

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1 hour ago, disturbman said:

there were hidden consoles at the cab ends. I do not know if this system has been retained for the automation of line 1 and line 4.

on MP05, the hidden console is still there. They've stuck on top of the metalic cover a printed adhesive with a fake driving console for the children to play. Quite funny to see children 'driving' the line 1. 

 

JM

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35 minutes ago, JR East said:

I was not aware of this 'tapis de pilotage automatique' despite the father of a friend of mine was driver on line 1. Thanks for the information. 


Most people aren't. The only lines that were never equipped are line 10 and the two bis lines. If you know it exists, the tapis PA is pretty noticeable: http://siteperso.metro.pagesperso-orange.fr/cadre5980voi.html. I'm not even sure the RATP removed it from the line 1 and the Ouragan/OCTYS lines.

By the way, one of the reasons line 1 was fully automated when it was, was also because the tapis PA and the track-side signalization equipment were at the end of their life and needed to be renewed.

edit: Yes, the MP89CCs were delivered to line 1 starting 1997, before being moved to line 4 because of the automation of line 1 in 2011. Now they will move on to line 6 when line 4 is fully automated. Read somewhere that tests should start next Spring on line 6. Fully automatic operation on line 4 should start end of 2023 as per the revised calendar.

Edited by disturbman
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2 hours ago, disturbman said:

It will do it if the system is programed for it. In all honesty, 15 seconds does not seem to be that difficult to make up. Sander will probably know more, but I expect the schedule is made in a way that allows trains to make up for a few minutes of delays if weather and traffic conditions allow.

 

I'm humbled, but yes that should be the case. Though I wouldn't call myself an expert on timetables, though that isn't to say I don't find them interesting, but yes the timetable has always included padding in one form or another, ever since the opening of the shinkansen. Generally speaking, services are usually driven at about 5 to 10 km/h below the ATC limit, an have been since the opening of the first shinkansen, the timetabled times are calculated with this in mind, so indeed a short delay can be made up by driving close to or at the ATC limit, allowing for the train to catch up to the timetable again. Even during the first year of operation, when the operating speed was limited to a maximum of 160km/h because the roadbed still needed to settle, drivers were permitted to drive at the 210 km/h ATC limit (though 200 was usually the max) if they had to make up for a delay. And even after the operating speed was increased in 1965, it was still the norm to drive at a max of 200 km/h or lower even though the ATC limit was at 210.

 

During the 1990's and early 2000's though, there was a movement in creating tighter timetables, especially from JR West on the Sanyō Shinkansen, which competed more directly with the domestic airlines. However, after the Fukuchiyama line derailment in 2005, and the subsequent reveal of how JR West's punitive measure systems related to among others time keeping, combined with their tight timetables (in order to compete with the Kansai area private railways), had likely contributed significantly to the decisions of the driver, even the shinkansen timetables were given more padding.

 

Now to be fair, some of the fastest Nozomi services (and Hikari services before that) have less padding than say a Kodama service, however even for those trains there is still more than enough slack in the timetable to correct small delays. Even the '320 km/h' Hayabusa and Super Komachi services on the Tōhoku Shinkansen, top out at around 315 km/h where 320 is the ATC limit (JR East shinkansen generally seem to be observing ATC speed -5 from my observations).

 

 

So yeah, I agree with @disturbman, I don't see why an automated system wouldn't be able to let's say, provide an optimum driving profile when a delay is registered in the same way or perhaps even better (a computerised system is probably better at keeping to the edge of the ATC curve than most human drivers would be able to) than a human could. Like I said a part of the shinkansen operations is already done automatically, and while the NHK example mentioned is impressive, in a "cool Japan" kind of way (i.e. it is not necessarily as impressive as it is made out to be in the documentary, which if it is the documentary I think it is, was really lacking in depth anyway) I don't see any reason why it couldn't be replicated by an ATO system.

 

 

 

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Does anyone know how they deal with keeping clocks synchronized? Most places are using GNSS these days, but obviously the legendary punctuality of Japanese railways predates that by decades.

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TokyoImperialPalace

@mojoYou can probably have a read of the document below for yourself. Initially the time was distributed through clocks post offices which were synced using sundails at midday with a ten minute buffer zone between clocks considered acceptable. The post office would later-on adopt a longitude correction calculator and the telegraph to sync clocks at midday more accurately. https://www.sci-museum.jp/files/pdf/study/universe/2017/12/201712_04-09.pdf

 

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