This Is Not a Test (1962).

This Is Not a Test (1962).

Late one night on a rural road in the western US, a policeman sets up a roadblock and begins stopping all traffic. When several cars and a big truck have stopped, he and the others learn the reason for this roadblock........
This Is Not a Test is presently in the public domain in the United States, and has been released in numerous DVD formats, on its own or in collections of similar films.

Reference Link:

http://publicdomainmovie.net/movie/this-is-not-a-test

Movie Source: Internet Archive (archive.org)