Interesting that people are using the DC collision to rag on PTS or PTC. The systems are totally different. Problems found in the DC system cannot be connected in any way with the PTS/PTC systems being proposed for "real" railroads other than via a generalized Luddite tendency.

The DC system has Automatic Train Control, the trains normally run completely without driver involvement other than watching the doors at the stations to hold them a moment if somebody might get stuck, and the "detection" system is based on old-fashioned (with a few computerized updates) signal technology with additional detectors. That type of detection/signal system is used in one way or another in nearly every modern rail transit system that uses extensive private r/w, at least to run the signals and let "central" know where the trains are. Based on the news reports, the crash seems to have occurred because the detection system failed allowing the computer to try to drive a train through another one it didn't know was there. The driver apparently tried to stop using the "panic button" but there wasn't enough time, for whatever reason.

Per Google Maps, there are two Metro tracks at that station (the outside tracks are CSX/MARC), and the approach seems to be nearly straight for some distance. Can't tell, of course, where the trains actually were, but they do run pretty close together; in the Google satellite picture, one is in the Fort Totten station, and another is clear of the previous station on the way in. On one trip to DC I used their Metro, and in rush hour on the Red Line the trains were less than 2 minutes apart, so they definitely use the system to the limits of its design. I think the only comparable systems in terms of age and design are BART and LA's Red/Orange Line.