Procedures for Establishing Speed Zones: Background

Section 2: Background

Basic Speed Law

Transportation Code, Chapter 545, Subchapter H, “Speed Restrictions,” contains the following sections governing speeds in the state:

Section 545.351, Maximum Speed Requirements
Section 545.352, Prima Facie Speed Limits (see also Transportation Code, Section 623.101, Speed Limit: for Manufactured House or House Trailer Being Towed)
Section 545.353, Authority of Texas Transportation Commission to Alter Speed Limits
Section 545.3531, (repealed by L 2011, Chap 259(14). eff 6/17/11)
Section 545.3535, Authority of Texas Transportation Commission to Alter Speed Limits on Certain Roads
Section 545.354, Authority of Regional Tollway Authorities to Alter Speed Limits on Turnpike Projects
Section 545.355, Authority of County Commissioners Court to Alter Speed Limits (see also Transportation Code, Section 251.154, Maximum Reasonable and Prudent Speeds on County Roads)
Section 545.356, Authority of Municipality to Alter Speed Limits
Section 545.357, Public Hearing to Consider Speed Limits where Certain Schools Are Located
Section 545.358, Authority of Commanding Officer of United States Military Reservation to Alter Speed Limits
Section 545.359, Conflicting Designated Speed Limits
Section 545.360, Duty of Texas Transportation Commission and State Board of Education to Provide Information and Assistance
Section 545.361, Special Speed Limitations
Section 545.362, Temporary Speed Limits
Section 545.3625, Confidentiality of Violation Information: Fuel Conservation Speed Limit
Section 545.363, Minimum Speed Regulations
Section 545.364, (repealed by L. 1999, Chap. 1346(3), eff 9/1/99)
Section 545.365, Speed Limit Exception for Emergencies; Municipal Regulation.

Collectively, these sections are referred to as the “basic speed law.” The basic speed law is founded on the belief that the majority of motorists are willing to modify their driving behavior properly, as long as they are aware of the conditions around them. Speed zone regulations are based on Section 545.351, which states in part: “An operator may not drive at a speed greater than is reasonable or prudent under the circumstances then existing.”

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Prima Facie Concept

In Texas, all speed limits are considered prima facie limits. Prima facie limits are those limits that, “on the face of it,” are reasonable and prudent under normal conditions. To exceed a prima facie speed limit does not automatically constitute an infraction of the law, as reasonable and prudent driving behavior is, at times, possible at speeds in excess of the posted limit. However, the burden of proof of reasonable and prudent conduct under the existing conditions rests with the driver. To afford a driver this opportunity to exceed a prima facie speed limit recognizes the fact that any posted speed limit cannot adequately reflect the many different road conditions confronting the driver on the same highways at different times.

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Authority to Set Speed Zones

The provisions of the Transportation Code, Chapter 545, Subchapter H, Section 545.353, give the Texas Transportation Commission the authority to alter maximum speed limits on highway routes both within and outside of cities, provided the Procedures for Establishing Speed Zones are followed and the Commission determines that the speed being established on a part of a highway system is a safe and reasonable speed for that part of the highway.

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Higher Maximum Speed Limit

The Commission may establish a speed limit of:

75 miles per hour on any portion of the state highway system.
80 miles per hour on parts of Interstate Highway 10 and Interstate Highway 20 in Crockett, Culberson, Hudspeth, Jeff Davis, Kerr, Kimble, Pecos, Reeves, Sutton, and Ward counties, or
Up to 85 miles per hour on a highway designed to accommodate travel at the speed being established.

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Local Authority and TxDOT

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, Speed Zone Studies, 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, Speed Zone Design 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:

It is not an officially designated or marked highway or road of the state highway system.
It is a two-lane, undivided highway or part of a highway.

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.

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Value of Speed Zoning

Although comparative “before-and-after” studies indicate that speed limit signs actually have very little influence on the driver’s choice of speed, speed zoning is necessary and does serve a worthwhile purpose. Realistic speed zoning will serve to protect the public and to regulate the unreasonable behavior of an individual. Having recognized that normally careful and competent actions of a reasonable person should be considered legal, the Texas Legislature has passed legislation concerning speed zoning in order to assure this protection. If a speed zone is determined by the actions of the majority of drivers on a highway, then it is hoped that speed zoning will facilitate the orderly movement of traffic by increasing driver awareness of a reasonable and prudent speed.

Properly applied speed zoning can:

help drivers adjust their speed to the conditions
make enforcement easier by furnishing police officers with a reasonable indication of what is excessive speed
result in more motorists driving within the same speed range at each of the locations along the highway
reduce the frequency and severity of crashes when accompanied by enforcement.

The Michigan Department of Transportation made a study entitled “Comparison of Speed Zoning Procedures and Their Effectiveness” dated September 1992. The following are some of the study’s conclusions:

Posting speed limits within 5 miles per hour of the 85th percentile speed has a beneficial effect, although small, on reducing total crashes but has a major beneficial effect on providing improved driver compliance. (See Chapter 3, Speed Zone Studies, for a discussion on the 85th percentile speed.)
Posting speed limits more than 5 miles per hour below the 85th percentile speed does not reduce crashes and has an adverse effect on driver compliance.
Speed zoning should not be used as the only corrective measure at high crash locations in lieu of other safety improvements.
The use of radar to collect speed data appears to underestimate the 85th percentile speed by approximately 3 miles per hour.

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Guidelines for Selecting Speed Limits

All authorized entities using these procedures should observe the following guidelines when selecting speed limits:

Speed limits on all roadways should be set based on spot speed studies and the 85th percentile operating speed (see Chapter 3, Speed Zone Studies, of this manual). Legal minimum and maximum speeds should establish the boundaries of the speed limits. If an existing roadway section’s posted speed limit is to be raised, the roadway’s roadside features should be examined to determine if modifications may be necessary to maintain roadside safety.
It is appropriate for posted speed limits to be based on the 85th percentile speed, even for those sections of roadway that have an inferred design speed lower than the 85th percentile speed. Posting a roadway’s speed limit based on its 85th percentile speed is considered good and typical engineering practice. This practice remains valid, even where the inferred design speed is lower than the resulting posted speed limit. In such situations, the posted speed limit would not be considered excessive or unsafe.
Arbitrarily setting lower speed limits at point locations due to a perceived shorter than desirable stopping sight distance is neither effective nor good engineering practice.
If a section of roadway has (or is expected to have) a posted speed in excess of the roadway’s inferred design speed and a safety concern exists at the location, then appropriate warning or informational signs should be installed to warn or inform drivers of the condition. Slightly shorter than desirable stopping sight distances do not present an unsafe operating condition, because of the conservative assumptions made in establishing desirable stopping sight distances. It is important to remember that any sign is a roadside object and that it should be installed only when its need is clearly demonstrated.
New or reconstructed roadways (and roadway sections) should be designed to accommodate operating speeds consistent with the roadway’s highest anticipated posted speed limit based on the roadway’s initial or ultimate function.