The Camera's on Metro link can not be viewed from a moving locomotive, even a download can only take place when stopped.
This doesn't mean that he wouldn't have been caught texting while driving on occasions before the accident.
That's what I don't understand about cab cameras. You can't have someone watching every engineer in real time. That would be prohibitively expensive. Are you going to randomly watch tapes? How often? Sure, I guess that cab cameras would make it easier to reconstruct an accident, but here you're talking about preventing one.
Here's an idea: you could have the *passengers* watch the engineer. Put up screens in each car. The passengers would certainly have good reason to watch their engineer for free! You could have the same thing in airline cockpits -- it would be even better then the channel that some airlines have to let you listen to air traffic control. Sure, it would change the nature of the job, making it more performance art, but so be it.
I still don't buy the slippery slope fallacy. If you are at work, I fail to see how you have any right to privacy while you're working. What you do in your off-hours is completely different, though I will grant that people often assume privacy there when none exists.