Section 3: Safety EnhancementsAnchor: #i1005705
Resurfacing, restoration, and rehabilitation projects are to be developed in a manner which identifies and incorporates appropriate safety enhancements. Engineering judgement will have to play a part in determining the extent to which safety improvements can reasonably be made with the limited resources available. Traffic volumes are an important factor to be considered 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. Even relatively low-cost incremental safety enhancements can significantly reduce accident frequency and/or severity.Anchor: #i1005716
Transportation Research Board 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 offers suggestions for considering project specifics very early in the 3R design process. These suggestions are paraphrased as follows:
- At the beginning of 3R project
design, highway designers should assess existing physical and operational
conditions related to safety.
- Gather data to identify specific safety problems that might be corrected and compare this data with the system-wide performance of similar highways.
- Conduct a site inspection using experienced personnel to recognize the opportunities for safety improvements within the common operating conditions of that individual roadway.
- Determine and verify existing geometry such as roadway widths, horizontal and vertical curvature, intersection layout, and other geometrics specific to the roadway section being examined.
- In addition to pavement repairs and geometric improvements,
designers of 3R projects should consider incorporating other intersection,
roadside, and traffic control improvements that may enhance safety.
- At horizontal curves where reconstruction cannot be accomplished, designers should evaluate less costly safety measures such as widening narrow pavements, flattening steep side slopes, removing or relocating roadside obstacles, or installing traffic control devices and pavement markings.
- Whether or not bridge widening is necessary on a particular project, designers should routinely evaluate guardrail installations at the bridge approaches, existing bridge rails for rehabilitation or replacement, and approach signing or delineation for inclusion in the project if appropriate and cost effective.
- Before developing construction plans and specifications, designers should document the project evaluation and give the design criteria which will be used to produce the final rehabilitation project.
Other methods have been successfully used to identify potential accident problems. These may be used at the designer’s option to meet the particular needs of the project.
- Maintenance personnel are normally more familiar with a particular route and can point out problem areas to the designer based on their experiences. These individuals frequently “work” accident locations and are called upon to perform corrective work necessitated by accidents.
- A traffic accident analysis can be conducted from reports generated using the Traffic Accident Information and Hazard Elimination Program volume of the Traffic Operations Manual. Additional information is available from the Traffic Operations Division or from District Traffic personnel.
- Accident locations can be hand plotted on a straight-line drawing of the roadway in question. If a location or type-of-accident cluster is found, a more detailed review should be undertaken to determine potential causes of the accidents. If similar causes appear frequently, corrective measures should be designed into the 3R project.
A summary of the accident evaluation should accompany the submission. This evaluation should document the presence, or absence, of any major deficiencies which may contribute to accident frequency and/or severity. This evaluation should be initially considered when scoping work in order that corrective measures may be taken where practicable.Anchor: #i1005807
Project Specific Design Information
The Project Specification Design Information has been developed to assist in the project evaluation and provide one possible outline for file documentation.
For individual project evaluation:
- Has an on-site evaluation of the project been conducted (date, time, personnel)?
- What is the highway type (low volume two-lane, urban street, etc.)?
- What are the design guidelines given in this chapter which are applicable to this project?
- What are the design values present on the existing roadway?
- What are the expected design values of the roadway after project completion? Which design elements require individual evaluation prior to final design?
- What is the ADT and the character (truck %, recreational use, local traffic, etc.) of the traffic using the roadway?
- What is the accident history (type, severity, conditions, etc.) of the entire project and at any specific locations which require the individual evaluation of design elements?
- What is the compatibility of the proposed design with
adjacent sections of the roadway?
For specific design elements which require individual evaluation prior to final project design:
- What length and percentage of the project is affected by the design elements in question?
- What is the comparative cost of the given design guideline versus the proposed design element in terms of construction, right-of-way availability, project delay, environmental impacts, etc.?
- What is the long term effect of using the design element selected in terms of capacity and level of service?
- If other design elements required individual evaluation, what is believed to be the cumulative effect of these design elements on the safety and operation of the proposed facility?
Basic Safety Improvements
Basic safety improvements will be required for all 3R projects. Basic safety improvements are defined as upgrading guardrail to current standards, providing signing and pavement markings in accordance with the Texas Manual on Uniform Traffic Control Devices, providing a skid resistant surface, and safety treating cross drainage pipe culverts 36 inches [0.9 m] in diameter or smaller that are inside the horizontal clearances 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 horizontal clearances. Consideration may also be necessary for trees, utility poles or other obstacles where these features are indicated significantly in an accident evaluation.
Guardrails. Guardrails shall be upgraded to current hardware standards. Connections to structures, post spacing and end treatments shall meet current design practices. Where guardrail height is 3 inches [75 mm] or more too high or too low, corrections in height are required. Guardrail will generally be installed to length requirements given in Determining Length of Need of Barrier in Appendix A.
All guardrail that is not needed should be removed. Guardrail also should be removed where obstacles being shielded may be cost effectively design treated (removed, made yielding, etc.).
Headwalls. Headwalls on small (36 inches [0.9 m] or less) cross drainage pipe culverts that are inside the horizontal clearances given in this chapter should be removed and sloping (1V:3H or flatter) culvert ends that blend with existing side slopes should be installed. Where located behind guardrail, these culvert ends should be safety treated and guardrail removed where there are no other obstructions involved. Where guardrail is required for shielding other obstacles, headwalls behind guardrail need not be safety treated. Also, where other non-removable, non-treatable obstacles are present near these culvert ends, culverts need not be treated.Anchor: #i1005918
Other Safety Enhancements
Cross drainage box and pipe culverts. Cross drainage box and pipe culverts greater than 36 inches [0.9 m] may remain as they exist where the horizontal clearances given in this chapter are satisfied. Where the horizontal clearances given in this chapter are not met, safety treatment (grates, extension, or guardrail) will be required. Where the culvert end creates a safety obstacle that is out of context with the remaining portion of the project, even though it meets clearances, consideration should be given to safety treatment. On the other hand, where other non-removable and non-treatable obstacles are located near culvert ends, treatment of culvert ends would be out of context with the immediate area, and guardrail or non-treatment may be the only choices.
Culverts. For culvert spans from 3 ft [0.9 m] to 5 ft [1.5 m] and heights up to 5 ft [1.5 m] that need to be safety treated, the 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 inlet restrictions (entrance loss coefficients) should be evaluated as to their effects on hydraulics. If necessary, reference can be made to the Hydraulic Design Manual for entrance loss coefficients with various configurations as well as other hydraulic design information.
Driveway embankments and pipes. Treatment of driveway embankments and pipes will be required on 3R projects only where other design improvements necessitate their reconstruction or when they are located inside the horizontal clearances 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, more significant geometric and safety related improvements may be appropriate.