Safety and Operational Impacts of Design Element Trade-Offs

First, we propose to review the existing literature identifYing and documenting the relationships that have been established between the various roadway geometric features and safety and operational levels. Specific design elements have been evaluated singularly or in combination with other elements and their safety consequences have been determined. Several ofthese studies were discussed in the previous section and specific points are also presented in Task 1. Second, we will identifY 10-15 states that have had design exceptions and maintain adequate crash data as well states where projects with design flexibility have been identified and documented. These states will be selected based on the available design exception documentation, projects with design flexibility, variety of design flexibility elements, the availability of safety data and records, and time since implementation ofthe design exception. These states will be selected among the FHWA Highway Safety Information System (HSIS) member states, ITom a review of a survey of the states completed in our previous work in NCHRP 15-22, ITomour case study documentation in FHWA-OI-IF (31), and IToma review ofthe survey on NCHRP Synthesis 316 (6). A fundamental component for selecting a state is the availability and accessibility of their crash databases. Third, upon completing an examination of the projects with design exceptions and design flexibility, including traffic information, geometric data, and safety records, we will conduct a safety and operational assessment of each project. This will result in the development of rational decision tools based on quantitative and semi-quantitative data analysis. In addition, special analyses will provide classifications by traffic volume and roadway type. Special information tools will provide further insight and perspective from past research. This information in practical, easy to use and understand format will allow roadway designers to assess the safety risk and choose a design element value consistent with the other needs of a project.