My take from my blog:

Everyone who writes about it notes that the script of the 1951 noir Roadblock makes no sense whatsoever, and everyone is right. In particular, the motivational 180s that have to be navigated by stars Charles McGraw and Joan Dixon beggar belief (as cool as it is to see McGraw in one of his occasional leads).

But the movie is iconic anyway for its famous closing sequence, one of the first to exploit the concrete channel of the Los Angeles River, then fairly new (in fact, parts were still under construction).