OK, I take the points. I never ever dismiss loss of life nor valiant efforts of emergency service personnel. My thoughts were that such instances as referenced were all predicted at the time, it's not just my hindsight, and today the predictions would be far more accurate.
The facts are that people ignore warnings, both chronic (this situation is likely to get worse and you'd be well advised to take precautionary action) and acute (it's happening now and jump to it!). How often have you witnessed a fire alarm go off and people just look at each other and think "is this really happening or is it just a false alarm, I'll just sit here for a bit longer and see if anyone else does anything."
We see numerous examples time and again of people ignoring specific warnings of approaching forest fires and waiting till the last moment before trying to drive through the flames, California for example. People don't even take any notice of red crosses showing closed lanes on motorways.
I know i'm a congenital skeptic, but I'll make a prediction that if it ever gets used in anger, most people will ignore it anyway. I still can't really think of a national emergency situation in which it would actually achieve anything, when it goes off what exactly are we supposed to do? I hope I'm wrong.
At the very least it can't really make things any worse I suppose, and as you say it might just save one life.
A warning sent to mobile phones when a driver tries to use one might be a good idea.
Best wishes to all