Check out this piece in the Economist.
It refers to Jim Speta’s excellent article, which sets forth:
three broad historical justifications for applying common carriage to regulate prices and access. First, many transporters enjoy a natural or state-granted monopoly and need to be restrained from exercising it with too much abandon. A medieval innkeeper, for example, often offered the only lodging in town; a boatman could cross only with the king’s writ. Second, the state sometimes offers favours of its own to transporters — public lands and roads, say, or the seizure of private property to make way for new infrastructure and expects a certain level of public service in return. Third, transport is essential to commerce. It represents an input cost to almost all businesses, and to restrict access or overcharge is to burden the entire economy.
I would hasten to add that the third justification is perhaps a bit understated, at least in the context of our modern problem. As I have said here and elsewhere at greater length, it is important to recognize (even if this has not been recognized historically) that (i) transport infrastructure is essential to much more than commerce, e.g., political and social engagement among communities, communication of ideas, news, etc., and (ii) many of the activities for which transport is essential (including commerce) generate substantial spillovers (social returns in excess of private returns captured by the actors engaging in the activity). Both of these extensions may be even more significant, in my view, when we shift from transport of people and physical goods to bits (information, data, speech, communications), in part because the bits are often themselves essential inputs and also because the bits are nonrivalrous in consumption and can be shared and used and reused productively.