<p>I think mathmomvt is right (post #5): the key here is to see what percentage of freshmen live on-campus. At many schools it’s just customary for most upperclass students to live in houses, apartments, co-ops, or fraternity/sorority houses, usually in the immediate vicinity of the school. For example, at my alma mater, the University of Michigan, only 37% of undergrads live on-campus, but 98% of the freshmen do. So virtually all freshmen live in the dorms (or “quads” as they’re called at Michigan), and only a small fraction of the sophomores, juniors and senior do—mostly sophomores, I’d guess, with a smattering of juniors and seniors living and working in the quads as RAs. Everyone else moves off-campus. But they’re not “commuters” in any recognizable sense; their lives revolve around campus and its immediate vicinity. In fact, some of the “off-campus” residents actually live closer to the Michigan Union and the Undergraduate Library than some of the “quaddies.”</p>
<p>Contrast that with Wayne State University, a true commuter school in the heart of Detroit. There, only 32% of freshmen live on-campus. That gives you a pretty good idea that a large fraction of the students start out commuting from “home,” i.e., from their parents’ house. Not all those who start out living off-campus will be living at their parents’ house, of course; some may get apartments with friends, some may have been out of school for a while and commute from their own houses or apartments. But it’s a pretty safe bet that if 2 out of 3 freshmen start out living off-campus, a large fraction of them are living with their parents and commuting.</p>