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Section 3: Designing for Safety

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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 should 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.

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Safety Design

TRB’s Special Report 214, Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation, describes a safety conscious design process for 3R projects as follows:

“Significant improvements in safety are not automatic by-products of RRR projects; safety must be systematically engineered into each project. To do this, highway designers must deliberately seek safety opportunities specific to each project and apply sound safety and traffic engineering principles. Highway agencies must strengthen safety considerations at each major step in the design process, treating safety as an integral part of design and not as a secondary objective. These actions require that highway agencies devote greater resources to RRR project design. . .”

Special Report 214 recommends considering project specifics early in the 3R design process. These suggestions are paraphrased as follows:

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  • At the beginning of 3R project design, highway designers should assess existing physical and operational conditions related to safety.
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    • 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 Crash Records Information System (CRIS) reports on the project location for at least 3 previous years. Use the DRIS Comprehensive Safety Dashboard and CRIS Crash Trees to identify both targeted locations and systemic safety countermeasures;
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    • Conduct a hot spot analysis of crash data to determine if safety problems arise because of an animal vehicle collision;
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    • 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, as this is a natural pathway for wildlife movement; and
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    • 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.
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  • In addition to pavement repairs and geometric improvements, designers of 3R projects should incorporate other intersection, roadside, and traffic control improvements that enhance safety, including wildlife crossing structures.
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    • 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;
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    • Evaluate whether TMUTCD requirements are met and, if not, ensure the proposed design will meet the requirements; and
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    • Routinely evaluate guard fence installations at bridge approaches, and existing bridge rails for rehabilitation or replacement. Include approach signing or delineation if appropriate, regardless of whether bridge widening is necessary on a particular project.
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  • Before developing construction plans and specifications, designers should document the project evaluation, and the design criteria which will be used. Other methods have been successfully used to identify potential safety problems. These methods may be used at the designer's option to meet the particular needs of the project.
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  • 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. Carcass data collection information can be used to determine if there are natural pathways for wildlife movement.
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  • Conduct a crash analysis. Refer to Chapter 5 of the Highway Safety Manual (HSM) for diagnosis procedures to identify causes of collision, safety concerns, and crash patterns. Coordinate with Design Division-Traffic Simulation and Safety Analysis Section for further guidance. Additional information is available from the Traffic Safety Division. 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.
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  • Carcass data collection information can be used to determine if there are natural pathways for wildlife movement. Run a hot spot analysis of crash data to determine factors for safety problems, including vehicle crashes caused by animals.
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  • Before developing the construction plans and specifications, consult the 4-year District Safety Plan and applicable Strategic Highway Safety Plan (SHSP) strategies. A summary of the safety and operations evaluation should be included in the project files and be made available during plan review. This evaluation should document the presence, or absence, of any major deficiencies which may contribute to operational issues and frequency and/or severity. Use this evaluation when scoping work so corrective measures may be taken where practicable.

For needed Project Documentation information see Section 7.

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Basic Safety Improvements

Basic safety improvements will be required for all 3R projects. Basic safety improvements are defined as:

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  • Upgrading guard fence to current standards;
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  • Providing signing and pavement markings in accordance with the Texas MUTCD and the Traffic Safety Division’s Traffic Engineering Standard Sheets;
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  • Providing a skid resistant surface; and
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  • Safety treating cross drainage pipe culverts 36 inches in diameter or smaller that are inside the clear zones given in this chapter.

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. Trees, utility poles, or other obstacles that are indicated significantly in a crash evaluation should also be considered.

Guard Fence

Guard fence must be upgraded to current hardware standards. Connections to structures, post spacing, and end treatments must meet current design practices. Where guard fence height is 3 or more inches higher or lower than criteria, height corrections are required. Guard fence lengths will generally be designed to requirements given in Appendix A, Determining Length of Need of Barrier.

Remove all unneeded guard fence and guard fence where shielded obstacles may be cost-effectively design treated (removed, made yielding, etc.).

Headwalls

Remove headwalls on small (36 inches or less) cross drainage pipe culverts that are inside the clear zones given in this chapter and install sloping (1V:3H or flatter) culvert ends that blend with existing side slopes. Where located behind guard fence, these culvert ends should be safety treated and the guard fence should be removed where there are no other obstructions involved.

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Other Safety Improvements

Cross Drainage Culverts

Cross drainage box and pipe culverts greater than 36-in may remain as they exist where the clear zones given in this chapter are satisfied. Where the clear zones given in this chapter 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, reference TxDOT's Hydraulic Design Manual 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 regardless of clear zone, see Chapter 2, Section 7 for additional guidance.

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.

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