We could list them on the site but with just a comment "no vehicle in this movie"... Thought that would be a little strange. Or I could add a flag "does not contain any car", so these movie could be listed separately. But then it would be useless (as you would not find it by searching "normal" movies).
And what about a movie that has only background cars, but that none is interesting enough to be listed? It could not be listed as "does not contain cars".