If all competitors were too, and we internalized all externalities, sure. But personal car travel is currently heavily subsidized (no, the fuel tax does not cover road costs), and has some serious negative externalities (both from air pollution, and traffic accidents being the leading cause of death for people under 30).
We demand that public transit be self-sufficient, while subsidizing private personal transportation. The market is a great "figure out the most efficient solution" mechanism, but not if you skew it in favor of one particular solution as we're doing now.
