Said Placentia, meant Burbank (the SUV episode), but similar concept holds for Placentia. If Metrolink has PTC but BNSF/UP doesn't, how does the Metrolink train really know what's happening out there if the non-equipped train does something strange? The magic system has to be used by everybody, not just one entity, for it to work - hence the FRA and Congressional compulsion.

For now, ATS and training and better supervision have to make up for everybody (not just Metrolink) not having PTC. It can be done - many other commuter systems don't have PTC but don't have wrecks between trains either, at least not as often as Metrolink seems to crunch things. Even in Chicago traffic. Not counting grade crossing wrecks - just train-on-train. Seems like something's going on at Metrolink that won't necessarily be fixed by PTC.

Frankly, ATS on the Metrolink wouldn't have prevented Chatsworth. Slowed it down perhaps (more survivable?) but not prevented. ATS in its traditional and simplest form only acts after you've run the red. PTC *might* have prevented it if it were enforcing everything including what the signals were supposed to say, but even then if the train ran thru the points into single track with the freight coming down the hill the hit would have happened; PTC would have to actually stop the train short of the signal overriding any engineer inputs to prevent the wreck. As we've seen in DC even full-on ATC isn't infallible. Welcome to the real world. You can use all the technology you want, and it helps, but the Mark I eyeball and attention between the ears are still needed.