Why can GPS issues delay a train 45 minutes?

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This is the second time I’ve been significantly delayed on the San Joaquins between Martinez and Antioch. Today was 45 minutes. Train personnel ascribe the delays to a computer issue, requiring involvement of the help desk. Today the engineer stated it was a GPS problem. How can GPS deficiencies delay a train?

Thanks…
 

zephyr17

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This is the second time I’ve been significantly delayed on the San Joaquins between Martinez and Antioch. Today was 45 minutes. Train personnel ascribe the delays to a computer issue, requiring involvement of the help desk. Today the engineer stated it was a GPS problem. How can GPS deficiencies delay a train?

Thanks…
GPS is required for PTC to work.
 
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Specifically PTC of the I-ETMS variety, which is operative on that route.
PTC = Positive Train Control, which enforces speed restrictions and distances between trains.

I-ETMS = one of several different means of implementing PTC. (I'm not familiar with it, but that's my assumption from the context.)
 

jis

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PTC = Positive Train Control, which enforces speed restrictions and distances between trains.

I-ETMS = one of several different means of implementing PTC. (I'm not familiar with it, but that's my assumption from the context.)
Yes, and specifically relative to the usage of GPS, I-ETMS requires a location service typically using GPS. Other PTC systems like ACSES do not require a GPS driven location service since they get their location information from track mounted Transponders.
 
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How many Amtrak trains are dependent on GPS-based PTC? If GPS should go down, would all trains have to stop where they were until it comes back up again? Is there some backup program in place so that trains can continue to run without GPS? Are aircraft similarly affected by the loss of GPS?

In a different thread, someone mentioned the domino-effect on travel which begins with a single storm, a single broken down freight train, a single computer malfunction, etc. Apparently GPS can also be a factor.
 
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jebr

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How many Amtrak trains are dependent on GPS-based PTC? If GPS should go down, would all trains have to stop where they were until it comes back up again? Is there some backup program in place so that trains can continue to run without GPS? Are aircraft similarly affected by the loss of GPS?

In a different thread, someone mentioned the domino-effect on travel which begins with a single storm, a single broken down freight train, a single computer malfunction, etc. Apparently GPS can also be a factor.

The issue is almost never the wider GPS system (it's run by the US Space Force,) but rather something with the GPS receiver for the train or some interoperability or link specific to the setup used by the rail operator. There would be a lot more issues than just trains having to stop if the totality of GPS were to go down for any significant period of time.
 
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PTC = Positive Train Control, which enforces speed restrictions and distances between trains.

I-ETMS = one of several different means of implementing PTC. (I'm not familiar with it, but that's my assumption from the context.)
Yes, and specifically relative to the usage of GPS, I-ETMS requires a location service typically using GPS. Other PTC systems like ACSES do not require a GPS driven location service since they get their location information from track mounted Transponders.
I’ve been meaning to find a context to present this idea:
We ought to have a glossary of railroad terms which people can refer to. It would help many, myself included!

Unless this already exists and I’ve managed to avoid it.
 
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I want to chime in with my appreciation for all of the folks here who generously share their expertise. When I first started visiting this site, I knew nothing about the technical aspects of trains or Amtrak. Now I know next to nothing. So keep up the good work!
Ditto. But I love all the non-technical aspects of Amtrak - and all train travel.
 
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I’ve been meaning to find a context to present this idea:
We ought to have a glossary of railroad terms which people can refer to. It would help many, myself included!

Unless this already exists and I’ve managed to avoid it.
It exists:

 

west point

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GPS is a backbone of ocanic air travels. For ETOPS operation usually 5 different satelites need to be in view and for 4? hours past expected arrival time. May have changed since I flew. Aircraft having reduntant inertial referance units (IRUs) also may be different.

Maybe your trip would have a section that the delay would would cause a no longer dead (GPS) section with thenenough satelites in view.
 
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Are aircraft similarly affected by the loss of GPS?
One of factors in this discussion is tossing out "GPS" as a kinda catch-all any PNT (Positioning, Navigation, and Timing) process or system that is supported by GPS. (DHS even has a PNT program.)

In the case of rail transportation I think the "P" is key to maintaining situational awareness of everything that is (supposed to be) moving on the tracks -- for those systems that utilize GPS. So any breakdown in hardware, software, connectivity, etc. could stop the trains.

For aircraft, GPS can be used as a primary navigational aid, or a supplemental service. Because sidings on the airways are so few and far between [ ;-) ], pilots often have more than one way of determining their position and/or path. Broadly, space-based position and navigation enables three-dimensional position determination for all phases of flight from departure, en route, and arrival, to airport surface navigation.

The timing part is seeing more and more use in applications such as land-mobile communications. GPS-provided precision timing makes trunked radio systems more effective.
 
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Explore

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Update: San Joaquin train 710 arrived Bakersfield 2 hours late on a scheduled 6.5-hour trip. We got later and later. Train was restricted to 59 mph (vs. 79), and meets were screwed up. Train 712 caught up to 710 and was slightly delayed by it. Passengers for #4 had to be bused to Barstow.
 

jis

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The issue is almost never the wider GPS system (it's run by the US Space Force,) but rather something with the GPS receiver for the train or some interoperability or link specific to the setup used by the rail operator. There would be a lot more issues than just trains having to stop if the totality of GPS were to go down for any significant period of time.
The specific failure of MARC PTC was apparently caused by the failure of the backbone WLAN which connects many critical components together. It had nothing to do with the core GPS service per se. Trains could find out their position all that they wanted. What they could not get is track occupancy authorization. And without that basically your PTC won't allow you to enter any track segment. Yes, unfortunate but necessary effect of fail safe in automation systems.

If you were en route you would be allowed to proceed at reduced speed under special order, but you are not allowed to depart a terminal with inoperative PTC.

On the NEC this would have created the situation where the signal shows Green but your PTC won't clear you to move, and regulations do not allow departure with inoperative PTC. So you are stuck, while Amtrak trains happily run along.
 
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The issue is almost never the wider GPS system (it's run by the US Space Force,) but rather something with the GPS receiver for the train or some interoperability or link specific to the setup used by the rail operator. There would be a lot more issues than just trains having to stop if the totality of GPS were to go down for any significant period of time.
While I was still in the Naval Reserve (this was almost 30 years ago) I attended a briefing which discussed threat assessments and system vulnerabilities. One thing in particular that I remember was that, in the event of a major global conflict, most of the communications satellites would be taken out in short order by the major super powers. (At that time, international terrorists weren’t as technically sophisticated as they are today.)

Today, so many of our systems are dependent upon communications satellites that I’ve often wondered what would happen if someone would seriously mess with them and what procedures are in place in the event that we had to do without them.
 

allanorn

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How many Amtrak trains are dependent on GPS-based PTC? If GPS should go down, would all trains have to stop where they were until it comes back up again? Is there some backup program in place so that trains can continue to run without GPS? Are aircraft similarly affected by the loss of GPS?

In a different thread, someone mentioned the domino-effect on travel which begins with a single storm, a single broken down freight train, a single computer malfunction, etc. Apparently GPS can also be a factor.
Found out the hard way the Surfliner trains are. Was headed to LAX and we just left San Juan Capistrano and all of a sudden we ground to a dead stop. Apparently the train lost GPS entirely and it had to be rebooted.

There are ways around it but apparently Amtrak ops teams can't get the authorization to bypass it like they used to. (That's what was told to me by crew, so take that with a pile of salt.)

Aircraft can use other systems like RNAV but they are getting phased out eventually because GPS is so good and usually pretty darn reliable. Aircraft have pretty good line-of-sight to satellites so if GPS goes out there's usually something fairly bad going on.
 

jis

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I am almost certain that it was the PTC onboard system that had to be rebooted and then reinitialized by downloading the route data, which can take a bit of time. The GPS segment of it is one of the simpler parts that is less likely to fail just by itself.
 
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