The streets constructed, reconstructed, improved and maintained by the state shall be of a width and type that the department deems proper, but the width so constructed, reconstructed, improved and maintained shall not be less than eighteen feet (18'); and, in the case of resurfacing and maintenance, from curb to curb where curbs exist, or the full width of the roadway where no curbs exist.
T.C.A. § 54-5-202