According to my only living great grandfather, while growing up in the 1950's, he had only used seat belts while riding in a passenger airliner. At that time even race car drivers didn't use seat belts, not even roll bars.
That must have begun to change when Bill Vukovich died in the Indianapolis Memorial Day Race. He remember the pictures of Vukovich's overturned car with only a hand visible from under the car. I googled Vukovich hand. I clicked on images, and I saw a photograph of the hand
The first cars in which he remembers using seat belts must have been Air Force military cars and trucks, and, of course, also airplanes in the mid 1960's.
Recently I watched a movie, Mulholland Falls, with Nick Nolte as a tough, Los Angeles police police officer who intimidates out-of-town gangsters in an an attempt to make them leave town. It must seem like an unlikely plot, but Gramps says that he has heard police officers brag about how they do that sort of thing. For example, Gilbert Ortega, former police chief of Phoenix, Arizona used traffic enforcement to stop and delay mobsters as they drove from the airport to their destination in Phoenix.
But I digress.
Noltle drives what appears to be a 1949 Buick Roadmaster, which sets the movie in the early 1950's. Near the end of the movie Nolte and three other actors ride in a Dakota type aircraft (Civilian DC-3, Military C-47) (Shirley Temple called it the Good Ship Lollipop)
In the aircraft, Nolte and the other actors do not use seat belts. I might have found that odd, but Gramps says that he did ride one time in a C-47 which did not have seat belts. The plane was a Philippine Air Force aircraft on a flight from Manila Airport to Lubang International Airport, also in the Philippines. He had flown from Clark Air Base to Lubang in American Air Force C-47's, and they had seat belts. Sometimes they even had parachutes. Philippine Airlines used the DC-3 version of the plane and they had seat belts.
So, not having seat belts made him nervous, but they made the trip without incident.
Lubang Island has an interesting history. A Japanese straggler lived there for thirty years after World War Two, but that is another story.