Tex. Const. art. X, § 2

Railroads heretofore constructed or which may hereafter be constructed in this state are hereby declared public highways, and railroad companies, common carriers. The Legislature shall pass laws to regulate railroad, freight and passenger tariffs, to correct abuses and prevent unjust discrimination and extortion in the rates of freight and passenger tariffs on the different railroads in this state, and enforce the same by adequate penalties; and to the further accomplishment of these objects and purposes, may provide and establish all requisite means and agencies invested with such powers as may be deemed adequate and advisable.