Car (bug?) breaks through floor of bridge; Beeps all the way down...

Ok, this has been driving me nuts since I was a kid.

I've googled every which way I can imagine.

Here are all the issues I can think of (not in order of importance):

1. I think I saw it sometime in the 70's (as a young kid).
2. It may be a movie short, that I saw in a drive-in theater with my parents.
3. Perhaps post-apocalyptic?
4. There's a car on a bridge. Perhaps a Volkswagon Beetle.
5. Floor of the bridge looks like it's covered in sheets of plywood.
6. Car suddenly breaks through the bridge floor and goes "beep beep beep..." all the way down.
7. Camera stays on the bridge, so we don't see the car actually hit anything.

What on earth was this movie? None of my friends have seen it, but my father remembers the scene, but cannot place it.

Sincerely,
Going nuts for over 40 years now.

One of the Herbie the Lovebug movies? There were a bunch of them.

I remember the film being fairly thematically dark, but that could have been the age I saw it. My parents used to take us to totally age-inappropriate movies back then, so this could have been an R rated flick for all I know. They'd cover our eyes for the bad parts. LOL.

It might even have been a trailer for a film.

You know what has occurred to me? There used to be these weird trailers for Alfred Hitchcock movies coming up. He would appear in the trailer oddly, but often not in the movie in that way.

For instance, in Frenzy, he was standing on a bridge looking down on a floating body strangled with a necktie and said "That's my tie!" This was not in the movie.

Perhaps it was something he took liberties with in a trailer?

ALSO, one of the weird car centric movies I [should not have] seen as a kid was "Vanishing Point". Dismal film that one. I wonder if it was there?

Still no luck. Sigh. Giving up. :-/