The GPS, radio communication, etc., that the article talks about are not the important bits of positive train control IMO. The important bits are "positively" enforcing safety -- reaching a safe state even if a rail vehicle violates the instructions the signalling system provides it. America's PTC mandate was triggered by the tragic Chatsworth crash back in 2005 or so, which would have been prevented if the red signal shown to the distracted train operator had been positively enforced.
1920s technology can provide enforcement. New York City subway and the Berlin S-Bahn both use old-school wayside trip cocks that raise next to red signals, and if a train passes a red, a mechanism on the side of the train strikes the raised trip cock, triggering a mandatory emergency brake application.
1920s technology can provide enforcement. New York City subway and the Berlin S-Bahn both use old-school wayside trip cocks that raise next to red signals, and if a train passes a red, a mechanism on the side of the train strikes the raised trip cock, triggering a mandatory emergency brake application.