How does a train know where it is?

Discussion relating to the operations of MTA MetroNorth Railroad including west of Hudson operations and discussion of CtDOT sponsored rail operations such as Shore Line East and the Springfield to New Haven Hartford Line

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How does a train know where it is?

Postby roysmith » Thu Aug 10, 2017 5:33 pm

On the new M8 Metro North cars, the automated announcement system often gets confused. We'll pull into New Rochelle, and the thing will be saying we're at Larchmont, or whatever. In the age of GPS being able to tell me where I am to within a few feet, it doesn't seem like it should be very difficult to know which town the train is in. What's the story there?
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Re: How does a train know where it is?

Postby RearOfSignal » Fri Aug 11, 2017 4:13 pm

ASI uses GPS for location information. While there have been problems related to GPS outages in the past, most problems are due to the ASI system simply freezing and not catching up properly to itself. Cues such as doors opening and train movement, signal certain actions by the ASI system. Sometimes if these actions happen in quick succession or out of order the ASI system freezes up and can make the wrong announcement.
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Re: How does a train know where it is?

Postby cobra30689 » Mon Aug 21, 2017 12:27 pm

On the Nippon Sharyo cars that VRE runs, the auto announcements are synchronized by an axle pickup sensor in the cab car. From what I understand back in the beginning a train was run on both lines, with a tech monitoring wheel rotations between stops, and that rotation count was stored in memory. Actual door opening at the station tells the system that the train has arrived, then it works its voodoo from there. It does have its hiccups now and then (especially when there are multiple cab cars in the consist), but for the most part it works pretty well.
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Re: How does a train know where it is?

Postby DutchRailnut » Mon Aug 21, 2017 2:40 pm

with wheel wear that would be terrible inaccurate.
on MN cars it works in correlation between Conductor input (stations/vs skipped stations) and GPS .
If Conductors are in charge, why are they promoted to be Engineer???

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Re: How does a train know where it is?

Postby Literalman » Sun Aug 27, 2017 6:48 pm

When I was commuting on VRE (1997-2017) I often heard wrong station announcements. Some (such as announcing the station we'd just left) might have been owing to being out of calibration, but others (such as leaving Fredericksburg and saying that the next stop was Union Station, Washington, DC) were hugely inaccurate. Also, many times the computer advised us to transfer to Metro at the next station owing do delays ahead on VRE. The alert was never true, in my experience, and often the next station was 20 or 30 miles from Metro. I've also heard wrong announcements on NJ Transit, both for the wrong station and for a station that the train didn't stop at.
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