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Interactive Highway Safety Design Model (IHSDM): User Applications and Case Studies

Over the past 2 decades, State and local agencies—and their consultants—the Federal Highway Administration’s (FHWA) Office of Federal Lands Highway, and many others have used IHSDM for a host of applications. This page provides summaries of select applications/case studies.

The following projects—categorized into three types (nonfreeway projects, freeway projects, and programmatic/systemwide/systemic applications)—have used IHSDM to apply Highway Safety Manual (HSM) Part C predictive methods.

Expand each category for a full list of documented user applications. Included are 7 IHSDM applications summarized below for which FHWA has developed Safety Data Case Studies.

IHSDM Case Studies: Nonfreeway Projects

ALDOT’s West South Boulevard Redesign Safety Assessment

Safety Data Case Study (FHWA-SA-21-075):

Summary: This case study summarizes a safety analysis conducted by FHWA’s Geometric Design Laboratory (GDL), in collaboration with ALDOT and the FHWA Alabama Division. GDL used IHSDM software to assess the safety performance of West South Boulevard, a high-volume, high-speed suburban arterial in Montgomery, AL. This analysis supported a proposed access management design that included pedestrian improvements. The existing corridor lacked pedestrian accommodations but exhibited notable pedestrian activity and informal worn paths. The corridor also experienced a higher-than-expected number of crashes in recent years, particularly pedestrian crashes. GDL used the IHSDM Crash Prediction Module to predict annual crashes and compare the existing condition of West South Boulevard with the proposed redesign that included pedestrian safety improvements. The results of the data-driven analysis informed ALDOT’s decisionmaking on the project and increased confidence in the pedestrian safety elements selected for the final design. West South Boulevard represents a facility type that is common throughout the United States, especially where suburban and rural areas interface and mixed land uses are adjacent to major freeway corridors. This example showcases one way that data-driven safety analysis and crash prediction available through IHSDM can enable agencies to make informed investments in road user safety.

WisDOT’s WIS 75 Intersection Screening & Project Development Process

Safety Data Case Study (FHWA-SA-21-074):

Summary: This case study presents a safety analysis conducted by WisDOT at the intersection of State Highway 75 (WIS 75) and Plank Road (County Road A) in Racine County, WI. WisDOT proactively identified key safety needs early in the project development process and used a data-driven approach to evaluate the safety effects of potential alternatives. WisDOT applied IHSDM to evaluate potential alternatives and assess predicted crashes. With predicted outcomes based on several alternatives, WisDOT used IHSDM’s Economic Analyses Tool to identify the most cost-effective alternative to improve safety at the candidate intersection.

FHWA-WFLHD’s Yale-Kilgore Road Safety and Traffic Assessment

Safety Data Case Study (FHWA-SA-21-073):

Summary: This case study presents a safety analysis by FHWA’s WFLHD Highway Safety Team. WFLHD used IHSDM as part of the design process to rehabilitate Yale-Kilgore Road. The Yale-Kilgore Road corridor is a county-owned and operated two-lane undivided road located in Clark and Fremont counties in Idaho. The project corridor is an important recreational and commercial artery for the community. As a rural highway in and around a national forest, it has many unique challenges that may not exist in more urban and suburban environments. The Yale-Kilgore Road Safety and Traffic Assessment is a practical example of how the suite of IHSDM modules can support typical project development in an atypical context. Although the corridor is currently a mix of paved and unpaved surfaces, with speed and out-of-town traffic representing major concerns in both the present and the future, IHSDM assisted practitioners with the analysis tradeoffs necessary to make informed design and safety countermeasure decisions. The ability to analyze the corridor from a broad perspective (i.e., not crash prediction alone) allowed WFLHD to assess targeted improvements along the corridor, especially along segments of the corridor where the relative crash risk is highest.

INDOT’s State Road 37 Improvement Project

Safety Data Case Study (FHWA-SA-21-019):  

Summary: This case study presents an interchange alternatives analysis from INDOT. The analysis supported a multiagency planning and engineering effort that involved INDOT, the Indianapolis Metropolitan Planning Organization, Hamilton County, Town of Fishers, and City of Noblesville. These agencies identified State Road (SR) 37 from 126th Street in Fishers to SR 32/38 in Noblesville as a candidate for significant mobility and safety improvements. The SR 37 corridor project had two primary needs: 1) reduce existing and forecasted congestion at signalized intersections within the study area, and 2) reduce the crash frequency and rate at identified intersections. INDOT targeted five at-grade signalized intersections along the study corridor for interchange improvements. The safety analysis applied State-specific safety performance functions and crash modification factors derived from the American Association of State Highway and Transportation Officials HSM to predict crashes for “build” and “no-build” scenarios over a 20-yr period between 2018 and 2038.

INDOT separately analyzed individual facility types for the no-build and proposed designs using IHSDM, including mainline segments, intersections, entrance and exit ramps, ramp terminals, and crossing street segments.

The INDOT analysis encountered several key challenges, including technical inputs for the IHSDM software and the application of the HSM to future design alternatives; for instance, INDOT did not apply the Empirical-Bayes method due to the significant change in the design and operational performance of the corridor between the build and no-build scenarios. INDOT’s ingenuity and engineering judgment allowed the agency to navigate many of these challenges, and the analysis predicted that the build alternative, although originally proposed for its traffic operation improvements, should yield a safety benefit and reduce crashes compared to the no-build alternative.

Using Predictive Methods for a Corridor Study in Idaho

Safety Data Case Study (FHWA-SA-21-019):  

Summary: IHSDM was used to identify existing geometric deficiencies, specific locations requiring further evaluation or locations requiring possible design improvements, and potential safety issues on existing Idaho State Highway 8 (Idaho 8) corridor conditions.

ITD contracted with a consultant to conduct a comprehensive review of existing Idaho 8 corridor conditions. The review identified deficiencies related to traffic operations, roadway geometry and cross section, access control, and safety with an overall purpose of identifying and prioritizing operational improvements over a 10-yr period.
IHSDM was used to evaluate existing traffic, examine roadway geometry, and predict crashes using existing traffic, roadway geometry, and the corridor’s recent crash history.

IHSDM Case Studies: Freeway Projects

Michigan’s US 31 at I–94 Interchange Alternatives Analysis

Safety Data Case Study (FHWA-SA-21-020):

Summary: MDOT used an iterative approach to project development that used IHSDM to identify a preferred design alternative based on a broad suite of traffic, safety, and cost considerations. The strategic application of IHSDM enabled MDOT to assess different design alternatives and project assumptions to make data-driven decisions for the proposed US 31 at I–94 Interchange and surrounding network.


IHSDM Case Studies: Programmatic/Systemwide/Systemic Applications

Safety Analysis in Project Development in Louisiana

Safety Data Case Study (FHWA-SA-21-019):

Summary: LaDOTD used safety data and safety analysis techniques (including IHSDM) in a broad range of project development practices. The scope includes all public roads in Louisiana and multiple operations within the LaDOTD.