Amtrak's not the only train to get off track (with GPS)

[AmtrakBlue]

I'm looking at the live map for WMATA and there's a Silver train riding on the yellow/green line. Guess someone forgot to switch the GPS data.

 

[PaunchyPirate]

At least it's still ON a track of some sort. Ha.

 

[jis]

How do they manage to use GPS in tunnels? I suspect the position is determined by track mounted location transponders and on board distance from transponder measurement (similar to what ACSES uses) or something like that rather than GPS.

But it is true that someone forgot to update the association between train Id and route Id for that train.

 

[railiner]

How do they manage to use GPS in tunnels? I suspect the position is determined by track mounted location transponders and on board distance from transponder measurement (similar to what ACSES uses) or something like that rather than GPS.

But it is true that someone forgot to update the association between train Id and route Id for that train.

I don't know about GPS on trains, but my car has a factory GPS, that when it loses its satellite reception due to a tunnel or other blockage, relies on its own "internal navigation system" to keep track of my position. When exiting the tunnel, when the satellite reception is reacquired, it recalibrates. Usually very little correction is needed. I believe it relies on the cars speedometer and odometer to keep track...I doubt it would be sophisticated to us a gyro or accelerometers like an expensive aircraft INS would. A portable Garmin or Magellan I believe just goes blank when satellite coverage is lost...

 

[jis]

Modern subway trains have tracks and track mounted transponders identifying specific locations and distance measurement along specific track. Usually properly equipped trains have very precise information about where they are.

For main line I-ETMS uses GPS occasionally with additional help to nail down which specific track it is one. ACSES does not use GPS, it uses track mounted transponders.

 

[jiml]

I don't know about GPS on trains, but my car has a factory GPS, that when it loses its satellite reception due to a tunnel or other blockage, relies on its own "internal navigation system" to keep track of my position. When exiting the tunnel, when the satellite reception is reacquired, it recalibrates. Usually very little correction is needed. I believe it relies on the cars speedometer and odometer to keep track...I doubt it would be sophisticated to us a gyro or accelerometers like an expensive aircraft INS would. A portable Garmin or Magellan I believe just goes blank when satellite coverage is lost...

The car's compass (if equipped) is part of the equation as well.