It's not as if it's particularly difficult to tamper with traffic flow now, as it stands. Take down a stop sign, mess with traffic light signalling (popular in movies about terrorist madmen), just plain go up to a car and hijack it.
The crackdown on people doing this, however, is enormous. It makes it very unprofitable to do any of these things.
The crackdown on people doing this, however, is enormous. It makes it very unprofitable to do any of these things.