The altering of the general statewide maximum speed limits to fit existing traffic and physical conditions of the highway constitutes the basic principle of speed zoning.

Transportation Code, Chapter 545, Subchapter H, Sections 545.355 and 545.356, give counties and cities the same authority within their respective jurisdictions. Counties with a population of more than 2.8 million and cities have the authority to establish a prima facie maximum speed limit of 75 miles per hour. The law also provides that any speed zone on highway routes in cities established by Transportation Commission minute order will supersede any conflicting zone set by city ordinance.

Except in very unusual circumstances, the zoning on state highway routes within cities should only be set by city ordinance based upon the recommendations of TxDOT. The usual practice, even for speed zones established by city ordinance, is for TxDOT to make the necessary speed studies and recommend the most appropriate zoning to the city. Cities that have a traffic engineering staff may also make speed studies on state maintained highways and recommend proper zoning. The procedure is permissible, as long as TxDOT is afforded an opportunity to review and approve the recommended city zoning.

County commissioner courts and governing bodies of incorporated cities, towns, and villages may alter maximum

prima facie

speed limits on roadways under their jurisdiction in accordance with the provision of the Transportation Code, Chapter 545, Subchapter H, Sections 545.355 and 545.356 respectively. However, alteration of maximum

prima facie

speed limits on any designated or marked roadway of the state highway system (even within the corporate limits of a city or town) typically requires an engineering and traffic investigation (as described in Chapter 3, , of this manual) and the approval of TxDOT.

A county that increases the

prima facie

speed limit on a county road or highway is also required to conduct an engineering and traffic investigation. However, 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, the county commissioners court may declare a lower speed limit of not less than 30 miles per hour, if the commissioners court determines that the

prima facie

speed limit on the road or highway is unreasonable or unsafe.

County authority does not extend to any segment of the state highway system; however, the commissioners court of a county, by resolution, may request the Texas Transportation Commission to determine and declare a reasonable and safe prima facie speed limit that is lower than a speed limit established by Section 545.352 of the Transportation Code on any part of a farm-to-market or ranch-to-market road without improved shoulders located in that county.

The Transportation Commission shall give consideration to local public opinion and may determine and declare a lower speed limit on any part of the road without an engineering and traffic investigation, but the Transportation Commission must use sound and generally accepted traffic engineering practices in determining and declaring the lower speed limit. Sound and generally accepted engineering practices for these FM and RM roadways without improved shoulders are described in Chapter 3, Section 4, of this manual.

County Authority is different from the authority of cities, who may exercise concurrent authority subject only to commission override. In exercising their authority, cities must base any speed zones on engineering and traffic investigations, unless the roadway meets all of the following criteria:

If the roadway meets the above criteria, the city may declare a lower speed limit of not less than 25 miles per hour if the governing body determines that the prima facie speed limit on the highway is unreasonable or unsafe.

The authority of regional tollway authorities, regional mobility authorities, and the commanding officer of a United States military reservation to alter speed limits is addressed in Transportation Code, Sections 370.033, 545.354, and 545.358. These decision-making authorities are required to follow the speed zone procedures as adopted by TxDOT when altering, on the basis of an engineering and traffic study, speed limits on off-system turnpikes or on-system highways within the confines of a military reservation.