(a) Overview.   (1) Purpose. This subchapter provides the information and procedures necessary for establishing speed zones and advisory speeds on the state highway system.   (2) Applicability. This subchapter is intended for use by entities with authority to set speed zones. These procedures shall be followed by the department, cities, and commanding officers of the U.S. military reservations when establishing speed zones on the state highway system. Regional tollway and regional mobility authorities shall follow these procedures when establishing speed zones.   (3) Responsibilities.     (A) The department will:       (i) conduct engineering and traffic studies associated with the establishment of speed zones and advisory speeds;       (ii) request cities to pass ordinances or resolutions establishing speed zones when necessary; and       (iii) erect and maintain necessary speed limit and advisory speed signs and notify local enforcement authorities upon installation of the signs.     (B) Cities will:       (i) request that the district conduct engineering and traffic studies associated with the establishment of speed zones on the state highway system within the city limits or conduct the studies themselves; and       (ii) upon approval by the department, prepare and pass city ordinances or resolutions establishing speed zones.     (C) A commissioners court of a county by resolution may request, through the district office, that the commission determine and declare a reasonable and safe prima facie speed limit lower than that established by Transportation Code, §545.352, on any part of a farm-to-market or a ranch-to-market road that is without improved shoulders located in that county. (b) Background.   (1) Prima facie concept. In Texas, all speed limits are considered "prima facie" limits. Prima facie limits are those limits which on the face of it, are reasonable and prudent under normal conditions.   (2) Authority to set speed zones.     (A) Transportation Code, §545.353 authorizes the commission 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 the highway system is a safe and reasonable speed for that part of the highway. The commission may establish a speed limit of:       (i) 75 miles per hour on any portion of the state highway system;       (ii) 80 miles per hour on parts of Interstate Highway 10 and of Interstate Highway 20 in Crockett, Culberson, Hudspeth, Jeff Davis, Kerr, Kimble, Pecos, Reeves, Sutton, or Ward counties; or       (iii) up to 85 miles per hour on a highway designed to accommodate travel at the speed being established.     (B) 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.     (C) Transportation Code, §545.355 and §545.356, give counties and cities the authority to establish a prima facie maximum speed limit of 75 miles per hour within their respective jurisdictions. The law also provides that any speed zone on highway routes in cities established by commission minute order will supersede any conflicting zone set by city ordinance or resolution.     (D) Except in very unusual circumstances, the zoning on state highway routes within cities should only be set by city ordinance or resolution based upon the recommendations of the department. The usual practice, even for speed zones established by city ordinance or resolution, is for the department 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 so long as the department is afforded an opportunity to review and approve the recommended city zoning.     (E) County commissioner courts and governing bodies of incorporated cities and villages may alter maximum prima facie speed limits on roadways under their jurisdiction in accordance with the provisions of Transportation Code, §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, typically requires an engineering and traffic investigation in accordance with §25.23 of this subchapter (relating to Speed Zone Studies), and the approval of the department.     (F) 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 on 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.     (G) 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 commission to determine and declare a reasonable and safe prima facie speed limit that is lower than a speed limit established by Transportation Code, §545.352, on any part of a farm-to-market or ranch-to-market road without improved shoulders located in that county.     (H) The 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 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 §25.23(d) of this subchapter.     (I) 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, notwithstanding the type of road or street and whether the state highway system is involved.     (J) The authority of regional tollway authorities, regional mobility authorities, and the Commanding Officer of a United States Military Reservation to alter the speed limits are addressed in Transportation Code, §§370.033, 545.354, and 545.358. These decision making authorities are required to follow the speed zone procedures adopted by the department 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.   (3) Guidelines for selecting speed limits. All authorized entities using these procedures should observe the following guidelines when setting speed limits.     (A) Speed limits on all roadways should be set based on spot speed studies and the 85th percentile operating speed (see §25.23 of this subchapter). 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.     (B) 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.     (C) 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.     (D) 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.       (i) 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.       (ii) Any sign is a roadside object that should be installed only when its need is clearly demonstrated.     (E) 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. (c) Factors affecting safe speed.   (1) Introduction. This subsection discusses various factors influencing drivers and their perception of the safe speed at which to operate a vehicle. Because so many variables affect the safe operating speed of vehicles, it is not practical to consider each individually. These factors should be considered as a whole and weighed accordingly.   (2) Design and physical factors of the roadway.     (A) The design and physical factors of the roadway place a definite limitation on the safe operating speed of vehicles. These factors include:       (i) horizontal and vertical curves;       (ii) hidden driveways and other roadside developments;       (iii) high driveway density;       (iv) rural residential or developed areas; and       (v) lack of striped, improved shoulders.     (B) Chapter 5, Sections 2 and 5 of the Procedures for Establishing Speed Zones manual provides the methods that must be used to determine if a curve or an obstruction to sight distance requires an advisory speed restriction.     (C) The effects of such factors as lane width, condition of surface, type and width of shoulders, frequency of intersections, and roadside development are not so easily measured. As a general rule, especially on tangents, these factors will be measured on the basis of prevailing speeds as determined by speed checks.   (3) The vehicle.     (A) The mechanical condition of vehicles and their characteristics for accelerating, decelerating, stopping, and turning affect safe speeds.     (B) The body roll angle of different makes of cars and year models of the same make also affects the safe operating speed on curves.     (C) Braking capabilities of different vehicles, such as passenger cars, buses, and various truck-trailer combinations, are obviously different, and it would generally not be practical to post safe speeds for each group.     (D) Normally, the posted speed will be that for the passenger car.   (4) The driver.     (A) The selection of speeds to be posted will be aimed at the ability and performance of the average driver.     (B) Average driver ability is considered in the form of perception - reaction time in the calculation of critical approach speeds to intersections, crosswalks, and locations with limited sight distance and in determining the posting distance for signs.   (5) Traffic.     (A) The presence of other vehicles on the highway, including those which may be entering, crossing, turning off, or parked, affects operating speeds.     (B) The frequency of pedestrians is an important factor. This is especially true at intersections with limited sight distance and at approaches to crosswalks.     (C) The speeds shall be posted for off-peak hour traffic on an average weekday. This will require drivers to adjust their speeds to lower values at times of peak hour traffic at some locations.   (6) Weather and visibility.     (A) Speeds will normally be selected and posted for good weather conditions and dry pavement. Texas law, however, also provides for the posting of speeds for wet weather conditions.     (B) Except in cases where the statewide maximum legal limits are posted, speeds will normally be posted on the basis of daylight speed values determined under good weather conditions.     (C) When it can be shown that it is required during wet or inclement weather, a wet weather speed zone may be established by commission minute order.       (i) The wet weather speed limit should be posted in addition to the regular posted speed zone.       (ii) When appropriately signed, this wet weather speed limit will be effective during wet weather at any time during hours of daylight and darkness. (d) Accident reconstruction speed limits.   (1) Transportation Code, §545.3561, gives municipalities and counties the authority to temporarily lower prima facie speed limits at the site of a crash investigation using vehicular accident reconstruction. The municipality or county must use a transportation engineering official with experience establishing speed limits. For a municipality, the authority applies to a highway or part of a highway in the municipality, including a highway in the state highway system. For a county, the authority does not apply to a road or highway in the state highway system. Cont'd...