NYC Subway Signals: A Complete Guide (2012) | Hacker News Reader

NYC Subway Signals: A Complete Guide (2012)

nycsubway.org

52 pointsat1as9 comments

This article is somewhat out-of-date. The L & 7 trains were modernized to communications-based train control (CBTC) & automatic train operation (ATO) since 2006 & 2018 respectively. This allows for moving-block signaling, where a trains are separated by a distance, instead of fixed blocks of track. The legacy fixed-block signaling system is still retained as a fallback.

Can confirm.

While the CBTC already existed, I worked on the ultra-wideband positioning system originally demoed on the 7 line (and spent a lot of sleepless nights riding empty 7 line trains, testing out the system).

I wrote the original version of the system that would initiate the time-of-flight signals to the trackside UWB beacons and use multilateration to determine the train position (of both extreme ends of the full train) based on knowing the ECEF coordinates of those beacons, all written in C (with MISRA C restrictions) on what were basically Raspberry Pi compute modules.

Also wrote the app you can see a screenshot of at the top of this post:

https://www.masstransitmag.com/rail/railroad-signals-ptc-con...

That app was C++/QML/Qt-based, using OpenStreetMaps to visualize the position. Originally written just as a visualization tool to consume data that was part of a test/mockup system I made while writing the code (mostly in San Diego, so very far from the NYC tracks we did final testing on), but the visualization of how it found the train position based on time-of-flight distance calculations from the UWB beacons looked pretty cool so they ended up putting it up (receiving data from the real, live system) on monitors while doing the media demos back in early 2020.

Whatever became of the UWB positioning system? The trials appeared to be successful, but to my knowledge the system has not yet been adapted in NYC or elsewhere.

Thanks for the extra context!

Doesn't feel much like it day-to-day in the NYC subway, but glad things are indeed continuing to change

Very similar detailed site for the Chicago L. Here's the signals page, but a ton more to explore as well: https://www.chicago-l.org/operations/signals/signals.html

When the CTA inherited the elevated system in 1947, much of the system still operated "on sight", which depended on the motorman's comprehension of and compliance with safe following distances and the rules governing them.

I think I recall reading that this "on sight" operation continued for quite a while at least on some of the elevated track including the downtown loop where most of the lines converge. I would assume a few bad accidents prompted the upgrades to automated signaling and stop trips.

That logo though :) Tickled that the "Y" and only the "Y" reference NYC.

Lots of words for "chain in, rail out" as they say on Nauvis

A very interesting thing to read on a long NYC metro ride.

Reply on news.ycombinator.com