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RULE §25.23Speed Zone Studies

      (iv) Legislative or congressional action. Notwithstanding the volume of traffic, if legislative or congressional action results in the immediate increase in statewide maximum legal speed limits, then reasonable and prudent speed zones may be established by trial runs and engineering judgment in lieu of other speed check procedures provided in this subchapter. Speed zones established through this process should be rechecked in accordance with the procedure in subsection (e) of this section.

      (v) Additional roadway factors. The posted speed limit may be reduced by as much as 10 miles per hour (12 miles per hour for locations with crash rates higher than the statewide average) below the 85th percentile speed or trial-run speed (performed if 125 cars cannot be checked during the two or four hour speed check) based on sound and generally accepted engineering judgment that includes consideration of the following factors:

        (I) narrow roadway pavement widths - 20 feet or less, for example;

        (II) horizontal and vertical curves - possible limited sight distance;

        (III) hidden driveways and other developments - possible limited sight distance;

        (IV) high driveway density - the higher the number of driveways, the higher the potential for encountering entering and turning vehicles;

        (V) crash history along the location;

        (VI) rural residential or developed areas - higher potential for pedestrian and bicycle traffic; and

        (VII) lack of striped, improved shoulders - constricted lateral movement.

    (B) Local public opinion may also be considered on farm-to-market and ranch-to-market roads without improved shoulders (Transportation Code, §545.3535(b)).

    (C) The final decision on the amount of variation from the 85th percentile speed for a specific roadway should be based on the engineering judgment of the supervising engineer.

    (D) Speed limits should not be posted more than 10 miles per hour (12 miles per hour for locations with crash rates higher than the statewide average) below the 85th percentile or trial-run speed (performed if 125 cars cannot be checked during the two or four hour speed check) since unreasonably low speed limits have not been shown to be an effective way to control speeding. Allowing too great a variation would risk losing motorist respect for speed limits and traffic control devices.

  (6) Blanket lowering of maximum speed limits. Blanket lowering of speed limits may be justified to avoid non-compliance with direct requests from the federal government to lower the statewide maximum speed limit.

  (7) Trial runs.

    (A) For the trial run, an average passenger vehicle that is representative of most vehicles on the highway and a reasonably competent driver should be selected.

    (B) After the 85th percentile speeds and zone lengths have been selected, several trial runs should be made through the area in both directions driving at the selected speeds. This should show any irregularities in the zoning which need correction.

  (8) Location of regulatory speed limit signs.

    (A) Speed zones are legally described to the nearest thousandth of a mile (5 feet). Regulatory speed limit signs should be located within approximately 5 feet of the actual reference marker or milepoint defined in the minute order or city ordinance or resolution.

    (B) The locations of regulatory speed zones tied to speed changes should be examined carefully to ensure that signs can be erected within the 5 feet variation. If adherence to the 5 feet variation is not possible, the speed zone sign should be placed as close to the actual location defined in the minute order or city ordinance or resolution as practical. For example, if the reference marker or milepoint is located at an intersection, the regulatory speed limit signs should be located in accordance with standard procedures for placement of departure signing.

(e) Rechecks of speed zones.

  (1) Introduction.

    (A) The basic data on which speed zones are established are subject to change when conditions change, and established speed zones must not be considered permanent.

    (B) Physical improvements to the roadway, increased roadside development, and heavy increases in traffic volumes justify a recheck of speeds to determine whether the 85th percentile speed has changed enough to require a change in the zone speeds.

  (2) Frequency of rechecks.

    (A) Periodic rechecks of all zones are desirable at intervals of about three to five years in urban areas regardless of roadway improvements, roadside developments, or increases in traffic volumes. Trial runs or rechecks of every third speed check station may be made.

    (B) Rechecks in rural areas are desirable at intervals of five to ten years. In many instances, trial runs may be sufficient.

    (C) If the speed checks or trial runs indicate a need for revision of the zone, rechecks of speeds should be made at all speed check stations for that particular section.

(f) Environmental speed limits.

  (1) Existing environmental speed limits. Existing environmental speed limits created at the request of the Texas Commission on Environmental Quality (TCEQ) may be retained on the state highway system until such time as:

    (A) the TCEQ advises the department in writing that the speed limit is unnecessary; and

    (B) a speed study performed for the area finds that the existing environmental speed zone is not reflective of the 85th percentile speed as determined by procedures detailed in this subchapter.

  (2) New environmental speed limits prohibited. As per Transportation Code, §545.353(j), no new environmental speed limits may be created on the state highway system.

Source Note: The provisions of this §25.23 adopted to be effective December 9, 2004, 29 TexReg 11389; amended to be effective March 16, 2006, 31 TexReg 1728; amended to be effective May 20, 2010, 35 TexReg 3859; amended to be effective October 20, 2011, 36 TexReg 6968

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