10.3 Safety Enhancements
10.3.1 Overview
Resurfacing, restoration, and rehabilitation projects must identify and incorporate appropriate safety enhancements. Use engineering judgement to determine the extent to which safety improvements can reasonably be made with the limited resources available. Crash history and traffic volumes are important factors to consider when evaluating cost-effectiveness of potential safety improvements. Typically, safety improvements are the most cost-effective on roadways with higher traffic volumes. This does not imply that safety enhancements on lower traffic volume roadways are not to be considered. Low-cost safety enhancements can reduce crash frequency and/or severity on all roadways.
10.3.2 Safety Design Evaluation
Using a performance-based design approach to inform design decisions, processes and procedures provided in the
,
, and
may be used to estimate the effectiveness of design treatments in reducing crash frequency and severity, and their cost-effectiveness.
Opportunities to incorporate project specific treatments to potentially reduce crash frequency and severity should be considered early in the 3R design process.
At the beginning of 3R project design, highway designers should assess existing physical and operational conditions related to safety. The following treatments and assessments of these conditions are:
- Gather data to identify specific safety problems that might be corrected and compare this data with the system-wide performance of similar highways. This can be conducted by gathering reports on the project location for at least 3 previous years. Use the Comprehensive Safety Dashboard and Crash Trees to identify both targeted treatments and systemic safety countermeasures;
- Conduct a crash analysis. Refer to the and for diagnosis procedures to identify causes of collision, safety concerns, and crash patterns. Coordinate with DES-Project Delivery section for further guidance. Additional information is available from the Traffic Safety Division (TRF). Coordinate with District traffic personnel for more information on traffic safety and operational improvements. District traffic personnel have the expertise to suggest corrective safety countermeasures that should be designed into the 3R project;
- Conduct a site inspection using experienced personnel to recognize opportunities for safety improvements within the common operating conditions of that individual roadway. This could include carcass data collection details (either within TxDOT or by a county or city) to determine if safety issues may be arising, if this is a natural pathway for wildlife movement;
- Partner with maintenance personnel, local law enforcement, and EMS who are familiar with a particular route and can point out problem areas to the designer based on their experiences. These individuals frequently “work” crash locations and are called upon to perform corrective work necessitated by crashes;
- Determine and verify existing geometry such as roadway widths, horizontal and vertical curvature, superelevation, stopping sight distance restrictions, location and design of intersections, side slopes, clear zone recovery distances, and other geometrics specific to the roadway section being examined;
- Review the four-yearDistrict Safety Planand applicable strategies. This review may identify operational or safety issues to be aware of and corrective measures that may be taken where practicable 3R projects should be developed consistent with the District Safety Plan and SHSP strategies;
- If the analysis of crash history on an existing road identifies one or more crash patterns that are potentially correctable by a specific design improvement or it is anticipated that a safety improvement would reduce sufficient crashes over its service life to be cost effective, designers should consider potential improvements to the site that could be implemented in conjunction with the 3R project and select one or more alternative designs that may reduce the crash frequency and/or severity at the site for further evaluation. Refer to the for guidance on selecting countermeasures based on the crash patterns of interest and related crash contributing factors;
- In addition to pavement repairs and geometric improvements, designers should consider incorporating intersection, roadside, and traffic control improvements into 3R projects that enhance safety, including wildlife crossing structures;
- Evaluate less costly safety measures at horizontal curves where reconstruction cannot be accomplished such as widening narrow pavements, flattening steep side slopes, and removing or relocating roadside obstacles. Additionally, designers can consider High Friction Surface Treatment (HFST) to address deficiencies in curve radius or superelevation if good life-cycle cost benefits are determined;
- Evaluate whether requirements are met and, if not, ensure the proposed design will meet the requirements;
- Evaluate guard fence installations at bridge approaches, and existing bridge rails for rehabilitation or replacement;
- Consider approach signing or delineation if appropriate, regardless of whether bridge widening is necessary on a particular project;
- The TxDOT (found on the Safer by Design webpage on TxDOT.gov) uses proven safety measures that are based on the predictive methods included in the . This tool, however, is unique to Texas roadway facilities and provides quantitative scores that are specific to how a change in a roadway design feature may directly influence the safety performance of a roadway. This tool provides an approach for evaluating potential improvements prior to implementation. A safety score should be determined early in the project development process so that the designer can optimize the proposed safety performance. Refer to TxDOT’s for additional information on when the TxDOT Safer By Design Tool should be utilized. The tool should also be used anytime future geometric improvements are programmed;
- Before developing construction plans and specifications, designers should document the project evaluation, and the design criteria which will be used. Other evaluation methods not presented here have also been successfully used to identify potential safety problems. These other methods may be used at the designer’s option to meet the particular needs of the project;
- The level of safety analysis (i.e., crash analysis and assessment of design alternatives) should be commensurate with the scale of the 3R project. For smaller scale 3R projects, a less detailed safety analysis is sufficient. For larger scale 3R projects, a more detailed safety analysis is recommended;
The
further documents the recommended methodologies and procedures used in Safety and Benefit-Cost evaluations and analyses.
For needed Project Documentation information see
.
10.3.3 Basic Safety Improvements
Basic safety improvements will be required for all 3R projects. Basic safety improvements are defined as:
- Upgrading guard fence to current standards;
- Providing signing and pavement markings in accordance with the and the ;
- Providing a skid-resistant surface; and
- Safety end treating cross drainage pipe culverts 36 inches in diameter or smaller that are inside the respective clear zone.
Other safety improvements to consider include treatment of nonstandard mailbox supports, nonstandard luminaire supports, and nonstandard sign supports that are inside the suggested clear zones. Treatment of trees, utility poles, or other obstacles that are indicated during a crash evaluation should also be considered.
10.3.3.1 Metal Beam Guard Fence
Metal Beam Guard fence must be upgraded to current roadside safety hardware standards. Connections to structures, post spacing, and end treatments must meet current design practices, and standards. See
for specific guidance on Metal Beam Guard Fence requirements. Metal Beam Guard fence lengths will generally be designed to requirements given in
.
Remove all nonessential guard fence and guard fence where shielded obstacles may be cost-effectively design treated (removed, made yielding, slope regrading/improvement, etc.).
10.3.3.2 Headwalls
Remove headwalls on small (36 inches or less) cross drainage pipe culverts that are inside the respective clear zone and install sloping (1V:3H or flatter) culvert ends (a.k.a., safety treatments) that blend with existing side slopes. Where located behind guard fence, these culvert ends should be safety end treated and the guard fence removed where there are no other obstructions involved.
10.3.3.3 Cross Drainage Culverts
Cross drainage box and pipe culverts greater than 36-in may remain in place where the clear zones are satisfied. Where the clear zones are not met, safety treatment (grates, extension, or guard fence) will be required. In situations where the culvert end meets clear zone requirements, yet other culverts within the project limits are treated, consider safety treatment to provide consistency within the project area. Where guard fence is required for shielding other non-removable obstacles, headwalls behind guard fence do not need to be safety treated.
For culvert spans from 3-ft to 5-ft and heights up to 5-ft that need to be safety treated, pipe grated design is very effective from a safety standpoint and generally cost effective from an economic standpoint. If sloping or grated inlet designs are utilized for these low height and width culverts and their past performance has not been satisfactory, then evaluate inlet restrictions (entrance loss coefficients) for their effects on hydraulics. If necessary, refer to TxDOT’s
for entrance loss coefficients with various configurations as well as other hydraulic design information.
The ends of bridge-class pipes and culverts must be protected whether they are inside or outside of the clear zone, see
for additional guidance.
10.3.3.4 Driveway Embankments and Pipes
Treat driveway embankments and pipes on 3R projects only where other design improvements necessitate their reconstruction or when they are located inside the clear zones given in this chapter.
The extent of the safety improvement selected for a particular project may be influenced by the extent of other work. Where pavement improvements extend pavement life substantially, consider more significant geometric and safety-related improvements.