EDIT: Wait, CSS is short for Cab Signalling System, right? If it is then we just have some acronym confusion going on.
Yeah. CSS would have prevented the Chatsworth accident. It's proven technology and available for modest cost. Unfortunately the NTSB borwbeat congress into implementing their little technological wet dream.
Actually, I don't think CSS would necessarily have prevented Chatsworth, although it would certainly have mitigated it tremendously, since the Metrolink train would have been held to 15 mph as it approached the stop signal at TOPANGA. If the engineer had exceeded 15 mph (let alone the 40 or so he was reported to be doing), the train would have received a penalty application which would almost certainly have stopped it before reaching the signal. However, if the speed had been lower than 15, with the engineer not paying attention, he could still have passed the home signal and collided with the freight train, which had practically reached the interlocking by that time. Of course, the freight's cab signal would have dropped to restricting when the Metrolink train overran its own signal, and if the freight had been a mile or so away at the time that would also have mitigated the effects of the collision (or even prevented it if the Metrolink engineer had returned to the real world in time to notice that he had run a stop signal, and stop his own train). In the absence of cab signals, the freight train would not have had the benefit of any advance warning once it passed the previous signal, no matter how far away he was from TOPANGA. Unfortunately, since the collision happened within seconds of the time the Metrolink train overran the signal, there was no time for anything to prevent it. I hope all of the projected train-separation systems are focused on stopping a train before it reaches a stop signal, not after it has gone by it.