More relevant to determining the commuter population would be the percentage of frosh living on campus, since it is common for non-commuter frosh to live on campus. The percentage living on campus overall is commonly much lower because many non-commuter students live nearby off campus. Note: for CPSLO, 91% of frosh live on campus.
Obviously, this is not a perfect measure, but it may be the best available, because the common data set numbers do not distinguish between various types of off-campus living (i.e. commuting from living with parents versus living off campus otherwise).