This is not a Test (1962)

A lone police officer receiving orders to block a road leading into an unidentified city in California because it is about to fall under nuclear attack. Soon, he has detained several vehicles with a variety of occupants ranging from an elderly man and his granddaughter, to a man who has recently become rich and his alcoholic wife, to a trucker and a hitchhiker. The motorists and the police officer hear attack warnings over the police radio and begin to prepare for the inevitable bombing.