This is Not a Test (1962)

Plot:

This is Not a Test tells the story of a rural road in the western US where the policeman sets up a roadblock and stops all traffic. When several cars and a big truck have stopped, he tells everyone why: a nuclear attack on the US appears to be underway, and since they have the truck there, their best chance at survival is to use it as a bomb shelter. Time is short and tensions in the small group quickly rise.

This is Not a Test (1962) Review:

Futuristic Atomic-age film noir, shot, composed and scored professionally, albeit with a lower budget. It was made back in 1962 and serves as amazing portrayal of paranoia of an impending USSR nuclear missile attack on America and how it effected a number of motorists and a deputy sheriff stranded in the dark and cold California desert.

Directed by Fredric Gadette
Starring Seamon Glass, Aubrey Martin, Thayer Roberts