| (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. (2) In establishing the speed limit the municipality or county is not required to conduct an engineering and traffic study or comply with other provisions of this subchapter. To set the temporary speed limit the municipality or county must: (A) follow safety guidelines as developed by the department for setting regulatory construction speed limits in work zone areas; (B) provide notice to the department district engineer in the district in which the accident reconstruction is occurring at least 48 hours prior to the speed reduction; and (C) during the time that the accident reconstruction is being conducted, place and maintain temporary speed limit signs that conform to the Texas Manual on Uniform Traffic Control Devices and temporarily conceal all other signs that permit higher speeds and remove the temporary signs and concealments when the accident reconstruction is complete. (3) If a traffic lane will be closed to accommodate the reconstruction investigation the municipality or county must follow all department rules and guidelines on lane closures. (4) The department may remove any temporary speed limit signs or concealments of speed limit signs that remain if the municipality does not remove them and after the department determines that the accident reconstruction is complete. |
| Source Note: The provisions of this §25.21 adopted to be effective December 9, 2004, 29 TexReg 11389; amended to be effective March 16, 2006, 31 TexReg 1728; amended to be effective October 16, 2008, 33 TexReg 8557; amended to be effective October 20, 2011, 36 TexReg 6968 |
