There is value to be tapped by enabling infill development. And in order to tap that value, more space efficient modes of transport are required than cars on streets.
Now, consider the zoning that is in place in most suburban areas: single use, single user per lot, mandatory set-asides to decrease density and force up value per house in new developments through artificial scarcity, and as a side-effect spilling over into increase property values in existing residences, and often severe height limits except when loosened by specific (and often expensive to obtain in terms of required political contributions) waivers. All of that, whether imposed by town or city zoning or by property owners association agreements, falls under state regulatory authority.
Now, suppose that the state specifies that for any dedicated common carrier transport corridor above a certain service quality ~ start and and service times, frequency, service waiting times & capacity ~ there are zoning easements around the dedicated stops of that service.