The National Academies

NCHRP 15-34 [Completed]

Performance-Based Analysis of Geometric Design of Highways and Streets

  Project Data
Funds: $500,000
Research Agency: Pennsylvania Transportation Institute
Principal Investigator: Venky Shankar
Effective Date: 7/14/2006
Completion Date: 3/13/2010


The objective of this project is to develop a guide for performance-based analysis of geometric design throughout the development of a project. The guide should identify existing tools for estimating performance and illustrate their use. Further, the guide should describe additional tools or enhancements to existing tools needed for estimating performance and a plan for developing them.


The Task 4  interim meeting was held on February 5, 2007.  A second interim meeting was held on June 19, 2009 to review the work being done on the draft report. The work will be completed under a separate contract, NCHRP 15-34A.


Most highway and street design processes rely on standards that set minimum values or ranges of values for design features. These standards are intended to provide operational safety, efficiency, and comfort for the traveler, but it is difficult or impossible for the designer to characterize quantitatively how the facility will perform. For both new construction and reconstruction of highways and streets, stakeholders and decision makers increasingly desire reasonable measures of the effect of geometric design decisions on the facility's performance for all of its users.

Each agency has its own process for designing a highway or street. Three critical stages in the process are project initiation (i.e., setting the project's purpose, need, and scope), preliminary design (e.g., analyzing alternative designs and environmental impacts and setting design criteria), and final design (i.e., preparing the construction plans); these stages may have different names in different agencies. Although the expected performance of the facility is only one of the factors that must be considered in designing a highway or street, a better understanding of the expected performance should result in better decisions during these stages. Research is needed to provide the designer with the tools to evaluate the performance of different design alternatives objectively.


Task 1.
Describe the decisions related to geometric design that need to be made at each of the three critical stages in the project development process listed earlier in Background. Describe the data that are available and relevant to estimating the performance of geometric elements at each of these stages.

Task 2. 
Identify aspects of street and highway performance that are of interest to transportation project stakeholders and decision makers. These aspects should include, but are not limited to, safety, mobility, and accessibility. For each aspect, identify candidate performance measures that are sensitive to the geometric design.

Task 3. 
Review completed and ongoing research to identify tools for estimating the performance of a geometric design (e.g., Highway Capacity Manual, Interactive Highway Safety Design Model, Highway Safety Manual, and SafetyAnalyst). Based on the literature and the research team's experience, assess each tool's usefulness in performance-based analysis of geometric design.

Task 4. 
Submit an interim report, within 6 months, reviewing the work done in Tasks 1 through 3 and recommending a suitable number of performance measures and analysis tools for further study in this project. The report should also include a refined work plan for the remaining project tasks and a detailed outline of the guide.  Meet with the panel to discuss the interim report.

Task 5. 
Finalize the performance measures needed to make decisions at each of the three critical stages of the project development process.

Task 6. 
For existing analysis tools, describe their data needs and capability to estimate the Task 5 performance measures. Describe additional tools or enhancements to existing tools needed for estimating performance and identify the data needed to use the tools. Update the work plan for developing the additional tools and tool enhancements.

Task 7. 
For the data identified in Task 6, assess their availability and accuracy during the different phases of the project delivery process, both currently and in the near future.

Task 8. 
Describe a generic framework for managing the data and performance-measure information throughout the project development process. The framework should include functional descriptions of the analysis tools and interfaces to them.

Task 9. 
Develop a guide for performance-based analysis of geometric design throughout the project development process. The guide should focus on practical applications using currently available data and analysis tools, and it should also present a vision of a future system facilitating better decisions using better analysis tools and additional data. The guide should include case studies to illustrate the use of the approach at each of the three stages in the project development process. The case studies should describe collection of the needed data (and adjustments due to missing data), selection and use of the analysis tools, and use of the performance measures in decision making.

Task 10. 
Submit a final report that documents the entire research effort and includes the Task 9 guide as a stand-alone document. The report should identify recommendations for text changes in the AASHTO Policy on Geometric Design of Highways and Streets.

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