I heard that there were Rabbonim about 100 years ago who forbade cars, saying that they were dangerous. Does anyone know who they were?
I don't know who did, but it wouldn't surprise me if that was the case. At the time it was a very new, uncommon, and perceived-as-dangerous thing.
Psalms tells us that shomer psa'im Hashem, G-d watches over the "simple." We are allowed to take whatever our society deems to be normal risks. Today (in the US), that includes driving a car, assuming a well-maintained car, a competent, undistracted driver driving safely, seatbelts, and so on.
Anecdotally, it appears that Rabbi Moshe Feinstein (who was born in Russia over a hundred years ago), personally viewed cars as newfangled risks about which he wasn't crazy.