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20 Most of the procedures specifically outline safety as being a high priority and require detailed supporting authority for safety-related deviations from standards. All the states noted particular attention to the docu- mentation of all the safety aspects of the project. Care- ful analysis of the types of accidents that occurred prior to the project is required and thoroughly documented. If the recommended values are not used in the new de- sign, the mitigation strategies that were instead em- ployed must be thoroughly documented and discussed. C. Documentation of Mitigation Strategies If a project cannot be designed to meet the full val- ues recommended in AASHTO or internal publications, designers should consider how mitigation strategies may help to reduce safety or operational problems. The following chart is included in Washington State's Pro- ject Development Manual.87 This chart is an excellent checklist or guideline for a designer to use when evalu- ating mitigation strategies and as a beginning point for the documentation that is necessary to include in the permanent file. 87 http://www.wsdot.wa.gov/publications/fulltext/ projectdev/Deviations/DeviationMitigation.pdf.
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21 Deviation Mitigation Options for Designers Design Criteria Mitigation Measures Available Comments Horizontal Alignment Post Warning Signs Consistency of mitigation Post Speed Advisory choices through significant Install Chevrons lengths of corridors is encouraged Flatten Roadside Slopes in order to avoid confusing Improve Horizontal drivers. Sight Lines Improve Clear Zone Area Improve Superelevation Install Illumination Widen Shoulders/Pavement Lane Width Post Warning Signs or Permanent lanes on the Speed Advisory Interstate system must meet or Improve Delineation exceed 11' minimum width to Install Raised comply with FHWA criteria. Pavement Markings Restrict Vehicle Size if Appropriate Restrict Traffic if Appropriate Shoulder Width Flatten Roadside Slopes Consider routing pedestrians Improve Delineation to use an alternate route. Identify and Post Alternate Bicycle Route Consider Installing Rumble Strips Post Warning Signs Provide Occasional Turnouts Bridge Width Post Warning Signs Consider routing pedestrians Improve Delineation to use an alternate route. Post Speed Advisory Bridge Office input is Upgrade Bridge Barriers encouraged. Identify and Post Alternate Bicycle Route Restrict Vehicle Size if Appropriate Restrict Traffic if Appropriate Structural Capacity Post Warning Signs Bridge Office input is Post Load Limit Signs mandatory. Restrict Vehicle Size if Appropriate Restrict Traffic if Appropriate Identify and Post Alternate Route