I think a lot of people take this approach. I have a friend who lives 9 miles from work, and often drives partway and bikes the rest. Sometimes she bikes the whole trip. And sometimes she drives the whole thing--like this entire winter. It's a good strategy, to gradually get strong enough to do the whole thing, or maybe it's a long trip that probably won't ever be entirely replaced by biking because of time constraints, it can at least make parking much easier and reduce gas costs a bit.