Texas Transportation Code - TRANSP § 545.355. Authority of County Commissioners Court to Alter Speed Limits

(a) The commissioners court of a county, for a county road or highway outside the limits of the right-of-way of an officially designated or marked highway or road of the state highway system and outside a municipality, has the same authority to increase prima facie speed limits from the results of an engineering and traffic investigation as the Texas Transportation Commission on an officially designated or marked highway of the state highway system.

(b) The commissioners court of a county may declare a lower speed limit of not less than:

(c) The commissioners court may not modify the rule established by Section 545.351(a) or establish a speed limit of more than 70 miles per hour.

(d) The commissioners court may modify a prima facie speed limit in accordance with this section only by an order entered on its records.

(e) The commissioners court of a county with a population of more than 2.8 million may establish from the results of an engineering and traffic investigation a speed limit of not more than 75 miles per hour on any part of a highway of that county that is a limited-access or controlled-access highway, regardless of the location of the part of the highway.