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From Tech Transfer Newsletter
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The Interactive Highway Safety Design Model
The Interactive Highway Safety Design Model (IHSDM) is a suite of software analysis tools for evaluating the safety and operational effects of geometric design decisions on two-lane rural highways.
IHSDM checks existing or proposed two-lane rural highway designs against relevant design policy values and provides estimates of a design's expected safety and operational performance. IHSDM results support decision-making in the highway design process and help project planners, designers, and reviewers justify and defend geometric design decisions.
A product of the Federal Highway Administration's Safety Research and Development Program, intended software users include highway project managers, designers, and traffic and safety reviewers in state and local highway agencies and engineering consulting firms.
IHSDM's evaluation capabilities
IHSDM can check designs against relevant design policy values, estimate the crash frequency expected for a specified geometric design, and estimate other safety and operational performance measures (for example, 85th percentile speed and percent time spent following) that help diagnose factors that contribute to expected safety performance.
IHSDM currently includes six evaluation modules:
- The Crash Prediction Module estimates the frequency and severity of crashes on a highway based on its geometric design and traffic characteristics. This module supports efforts to identify improvement projects on existing roadways, compare the relative safety performance of design alternatives, and assess the safety cost effectiveness of design decisions.
- The Policy Review Module checks highway-segment design elements for compliance with relevant geometric design policies. It can be applied at several stages in the highway design process. For improvement projects on existing roadways, it can provide an initial assessment of how the existing geometric design compares to current design guidelines. For all projects, it can facilitate quality-assurance checks through detailed design and design review.
- The Design Consistency Module helps diagnose safety concerns at horizontal curves by providing estimates of the magnitude of potential speed inconsistencies. Design consistency evaluations provide valuable information for diagnosing potential safety issues on existing highways. These evaluations also provide quality-assurance checks of both preliminary and final alignment designs.
- The Intersection Review Module has diagnostic review capabilities. The diagnostic review is an expert system that systematically evaluates the existing or proposed intersection geometric design to identify potential safety concerns and suggest possible treatments to address those concerns. The Intersection Review Module can provide useful input to project scoping, preliminary engineering, and design review.
- The Traffic Analysis Module uses the TWOPAS traffic simulation module to estimate traffic quality of service measures for an existing or proposed design under current or projected future traffic flows. This module is particularly useful during project scoping and preliminary engineering to evaluate the operational performance of alternatives to two-lane cross-sections, including passing lanes, climbing lanes, and short four-lane sections.
- The Driver/Vehicle Module simulates driving behavior and vehicle dynamics on a two-lane highway, providing predicted time histories of speed and other response variables, along with statistical measures of safety-related performance metrics, via a simulation of single driver/vehicle combination.
How to acquire free IHSDM software
A free download of the current release of IHSDM software is available.
The website summarizes the capabilities and applications of the IHSDM evaluation modules. It also provides a library of the research reports documenting their development. More information and resources.
IHSDM training
The National Highway Institute (NHI) provides a two-day IHSDM training course (FHWA-NHI-380071).
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