They're working on a beacon-based train time system now [1]. Bluetooth beacons are installed on cars with trackside sensors as trains enter and exit stations. S

They're working on a beacon-based train time system now [1]. Bluetooth beacons are installed on cars with trackside sensors as trains enter and exit stations. Station wi-fi is used to relay data about entering and exiting trains. Since the MTA already has train speed and track length data, it gives a pretty accurate guess at where the train is between stations. It's not as accurate as full trackside sensors throughout the tunnels, but much faster and cheaper to spin up. Pretty clever overlay IMO. [1] http://www.metro-magazine.com/rail/article/715387/nyc-transit-uses-new-tech-tests-real-time-train-arrival http://www.metro-magazine.com/rail/article/715387/nyc-transi...