Really depends on where you are. When you want to ferry people between huge parking lots, sure, go for it. But ferrying people between parking lots is a band-ai

Really depends on where you are. When you want to ferry people between huge parking lots, sure, go for it. But ferrying people between parking lots is a band-aid at best, compared to a real transit system. Also, if above-ground space at the connected points is sufficiently cheap, you will usually find most of the connection to be cheaper above-ground as well.