In the half century of public regulation of railroads in the United States, regulatory legislation has dealt primarily with functions incident to the operation of existing enterprises. The basic concept has been that railroad corporations as common carriers have voluntarily assumed obligations to the public which the public has a right to require to be performed.
Kenneth F. Burgess,
Compulsory Construction of New Lines of Railroad,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol20/iss7/2