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tools for designing roadways where design flexibility may be other ongoing NCHRP projects on the development of the
appropriate to the roadway context. Highway Safety Manual (HSM) (7). The HSM is envisioned
The research was conducted in two phases. The first phase to be a comprehensive document of current knowledge related
comprised a literature review and the development of method- to roadway safety treatments as well as to contain tools for
ology for data collection and analysis in the second phase. In predicting the safety effects of different roadway design alter-
the second phase, data were collected and analyzed to develop natives for various classes of roadways. Several NCHRP projects
an understanding of the safety and operational impacts from were initiated in support of HSM development at the same
design element trade-offs. The two-phase project included time as Project 15-27, and efforts were undertaken to coor-
seven specific tasks: dinate with some of these projects to produce compatible
results. The project team worked very closely with the team
· Phase I Tasks of NCHRP Project 17-29, "Methodology to Predict the Safety
Task 1: Review of past and ongoing work relative to rural Performance of Rural Multilane Highways," which aimed
multilane highway crash prediction models and accident to develop predictive tools and the HSM chapter for rural
modification factors (AMFs). multilane highways.
Task 2: Development of data acquisition plan identifying
states with crash databases that could be used in the next
Organization of the Report
phase as well as specific data elements.
Task 3: Development of a data analysis plan for manip- This report presents the findings and conclusions of the
ulating the collected data and developing appropriate research to develop crash prediction models and AMFs for
prediction models and AMFs. specific design elements of multilane rural highways. The
Task 4: Development of an interim report and work plan. research results are included along with recommendations
· Phase II Tasks for future research. The remainder of the report is organized
Task 5: Acquisition of the appropriate data and analysis in the following chapters:
of the data to develop the appropriate models and AMFs.
Task 6: Development of guidelines that could be used · Chapter 2: Literature Review--presents the current knowl-
by designers in evaluating the safety consequences from edge on AMFs and identifies potential needs for the work
design element trade-offs for multilane rural highways. undertaken herein.
Task 7: Preparation of final report. · Chapter 3: Data Analysis--documents the methodology
followed to analyze the collected data, includes a description
The first phase of the project identified a plan for data col- of the data used, and presents the results from the analysis.
lection analysis that would produce reasonable models and · Chapter 4: Design Elements Recommendations--presents
AMFs for future use. The plan was reviewed by the NCHRP the proposed guidelines for the various design elements as
project panel, and adjustments were made to the direction of a result of this research.
the work. The major adjustment was a departure from the · Chapter 5: Conclusions and Suggested Research--includes
original objective of identifying the safety implications from a summary of the study objectives, project findings, and
several design elements and focusing only on several specific recommendations for future research work.
cross-section elements: lane width, shoulder width and type,
median width and type, and (possibly) clear zone width. This An appendix discusses the use of prediction models to
refocused approach allowed for a better coordination with determine the relative safety of design element choices.
