Following on from the previous post …
I think calling people-in-cars “people in cars” (rather than “motorists”) is slightly more useful than calling people-on-bikes “people on bikes” (rather than “cyclists”).
“Motorist” is more often used rhetorically as an appeal to solidarity in a way that “cyclist” is not – as in “stopping the war on the motorist” “this will hurt the motorist!” etc etc. Yet because of the ubiquity of driving, it is much less likely that any given individual in a car has any sort of serious “identity” that is built around driving. Many (most) people just go along with what society has made it easiest for them to do … (see the Gillian Anable research on attitudes to car use).
So perhaps better not to use a term that implies people do have some sort of meaningful identity as a “motorist” when they most likely do not? Spelling things out in this rather pedantic way might tend to emphasise the fact that we all make a variety of transport choices.