If all you had was good old fashioned ATS on the signal, the Metrolink would still have been able to blow through the red, bend the switch, and go up to the collision point assuming that the speed at the signal was 40+ to maybe 50 as reports suggest. Main difference would have been less closing speed, which might have let the first car absorb the impact rather than just burst open. What's stopping distance in emergency from, say, 45 mph - I'm guessing at least a couple of train lengths? Impact point was less than 1000 ft from the signal.

If there had been some kind of continuous monitoring based on signal indications, as appears to be installed in some light rail cars, it would have noted overspeed shortly after the train left the station (assuming a yellow block on Metrolink implies 30 mph or so) and perhaps done something about it before the red signal - but the train still probably would have slid into the single track section leading to contact with the freight though undoubtedly at a much lower speed. Hence the need for ALL trains to have the gear in PTC setups, if you want a reasonable chance of avoiding almost all wrecks. The freight people will scream bloody bankruptcy of course, since they want to run their power anywhere not just in LA. Hence the demand for some kind of national standard before anybody does anything.

The only way to truly prevent the problem is with full automatic train control where the computer drives not the engineer - a la BART. If you trust the computer and aren't too quick to switch to manual override. Unfortunately, the computer doesn't see too well so unless your RR is fully fenced off and grade-separated from anything/anybody that might randomly get in the way (a la BART) you need somebody in the cab to press the Big Red Button when it all comes unglued. Ain't gonna happen on Regular Railroads that wander alongside streets and through backyards. And I'm not too impressed by GPS-based systems either - unless repeaters of some kind are used ($$$$), GPS has to be able to see several satellites to know where it is, which gets a little challenging in hilly areas, big cities, forests, and tunnels (ummm ... California anyplace where you find people or Really Crowded Single Track Railroads?). Watch the GPS nav system in your car in downtown LA, for instance - it gets a little confused unless it's able to operate for a while on "dead reckoning" until the satellites reappear.

I'm thinking some kind of continuous monitoring at least on commuter trains is the way things will go. Might be a little pricey to install on older locos that aren't fully "drive by wire" even if the wayside gear didn't cost a ton - you're essentially looking at cab signals everywhere. I also see Metrolink having to pay out so much for this wreck (this one will easily top $1/2B by the time the lawyers are done) that they won't have money to keep running trains let alone invest in new/better signals. Higher taxes anybody?