Updating the Crash Modification Factors and Calibrating the IHSDM for Indiana

Abstract

The Interactive Highway Safety Design Model (IHSDM) is a tool for assessing the safety impact of project-level design decisions by implementing the HSM crash prediction methodology. Safety Performance Functions (SPFs), Crash Modification Factors/Functions (CMFs), calibration factors, and crash proportions are utilized in predicting the number, severity, and type of crashes occurring on various types of roadway facilities. This study updated and expanded the set of CMFs applicable to Indiana conditions for various geometric, traffic, pavement, and other road characteristics. CMFs for 80 various road and control improvements for urban and rural segments, intersections, and interchanges. This report also presents the methodology of calibrating the IHSDM's predictive components based on local data and past research. This method jointly estimates the SPFs and CMFs to preserve the crash prediction consistency. SPFs, CMFs, and crash proportions were calibrated for Indiana rural two-lane segments, rural divided multilane segments, and urban/suburban arterial segments. Example calculations showed that some results were only slightly affected while others vary considerably. This finding confirms the need for calibrating the parameters in the IHSDM to local conditions.

Crash Distribution Dataset: Development and Validation for the Undivided Rural Roads in Oromia, Ethiopia

“…Nowadays, CPM of the Interactive Highway Safety Design Model (IHSDM) software, which is developed by the Federal Highway Administration, is the commonly used predictive approach. IHSDM software incorporates the four predictive components of HSM, which are (i) safety performance function (SPF), (ii) crash modification factors (CMFs), (iii) calibration factor (Cx), and (iv) crash distribution dataset (Tarko et al, 2018). Thus, the constraints in the calibration of the predictive HSM components can be carried out by the application of the IHSDM tool (Tarko et al, 2018).…”

“…IHSDM software incorporates the four predictive components of HSM, which are (i) safety performance function (SPF), (ii) crash modification factors (CMFs), (iii) calibration factor (Cx), and (iv) crash distribution dataset (Tarko et al, 2018). Thus, the constraints in the calibration of the predictive HSM components can be carried out by the application of the IHSDM tool (Tarko et al, 2018). Many studies were made to assess the applicability of CPM in IHSDM software.…”

“…categorized by overall crashes, crash severity proportions, and collision type distribution). The predictive approach of HSM has four main features these are; Safety Performance Function (SPF), Crash Modification Factor (CMF), Calibration Factor (C) and Crash distribution dataset ((AASHTO), 2010; Tarko et al, 2018). SPF is a statistical model that predicts the crash frequency of facilities based on the specified base conditions (HSMs specified base conditions).…”

Statistical Analysis of Safety Improvements and Integration into Project Design Process

“…The IHDSM, although calibrated to the Indiana conditions in the recent JTRP study (Tarko et al, 2018) is suitable for large road projects in mind and it requires designers' significant effort for preparing and entering the input. Yet, it does not support sequential decisionmaking in the course of design but rather it facilitates a selection of the most promising alternative from several alternatives already designed.…”