Establishing performance-based safety goals and objectives becomes more attainable with the Highway Safety Manual (HSM). However, the safety performance functions (SPFs) in the HSM may not be accurate as they are not calibrated to local conditions. In addition, each SPF and crash modification factor (CMF) assumes a set of base site conditions which may not be realistic for local roadways. Although calibration procedures are available in HSM Part C Appendix A, they should be refined or modified to accommodate local data availability and roadway, traffic, and crash characteristics. It is also necessary to determine a set of base conditions applicable to local highways. This document presents the application of the HSM for rural local two-lane two-way highway segments in South Dakota (SD). The calibration was based on three-year (2009-2011) crash data from 657 roadway segments constituting more than 750 miles of roadways. The calibration process includes establishing new base conditions, developing SPFs, converting CMFs to base conditions as well as substituting default values with state-specific values. Five models have been developed and compared based on statistical goodness-of-fit and calibration factors. The same procedures were also conducted for the tribal two-lane two-way highway segments in SD based on three-year (2009-2011) crash data from 56 roadway segments constituting 199.5 miles of roadway. Results show that the jurisdiction-specific crash type distribution for CMFs can be drastically different from what is presented in the HSM. For rural local two-lane two-way roadways, the HSM method without modification underestimates SD crashes by 35 percent. The method based on SPFs developed from a full model has the best performance. For tribal two-lane two-way roadways, the HSM method without modification overestimates SD crashes by 122 percent. The method using the exponential from of annual average daily traffic (AADT) performs the best. This documentation provides important guidance and empirical results regarding how to calibrate HSM models.

The IHSDM is a suite of software analysis tools for evaluating safety and operation effects of geometric design decisions on two-lane rural highways. IHSDM provides highway project planners, designers, and reviewers in state and local departments of transportation (DOTs) and engineering consulting firms with a suite of safety evaluation tools to support these assessments. The goal of Subtask A.1.1 has been to conduct a preliminary human factors evaluation f the IHSDM interface using existing user-interface design principles.

The IHSDM is a suite of software analysis tools for evaluating safety and operation effects of geometric design decisions on two-lane rural highways. IHSDM provides highway project planners, designers, and reviewers in state and local departments of transportation (DOTs) and engineering consulting firms with a suite of safety evaluation tools to support these assessments. This report describes the activities and results associated with Task A.1: Conduct User Evaluation of the IHSDM Interface.

The Interactive Highway Safety Design Model (IHSDM) is a suite of software developed by the Federal Highway Administration (FHWA) for monitoring and analyzing two-lane rural highways in the United States. Among the six modules available in IHSDM, two were chosen for evaluation because of their applicability to audit safety of the two-lane rural highways in Utah, namely the Crash Prediction Module (CPM) and the Intersection Review Module (IRM). It was found that the CPM can produce reasonably reliable crash predictions if appropriate input data, especially alignment data, reflect the existing conditions at reasonable accuracy and engineering judgment is used. Based on the findings of the study, it is concluded that the CPM and IRM of IHSDM could be a useful tool for engineering decision-making during safety audits of two-lane rural highways. However, the outputs from these modules demand knowledge and experience in highway design.

The IHSDM is a suite of software analysis tools for evaluating safety and operation effects of geometric design decisions on two-lane rural highways. IHSDM provides highway project planners, designers, and reviewers in state and local departments of transportation (DOTs) and engineering consulting firms with a suite of safety evaluation tools to support these assessments. The goal of Subtask A.1.2 is to prepare a detailed workplan for conducting a user-interface evaluation.

IHSDM consists of six modules: Policy Review Module (PRM), Crash Prediction Module (CPM), Design Consistency Module (DCM), Traffic Analysis Module (TAM), Intersection Review Module (IRM), and Driver/Vehicle Module (DVM) (still under construction). Among the six modules, two were chosen for evaluation because of their applicability to audit safety of the two-lane rural highways in Utah, namely CPM and IRM.