Interactive design models help build safer roadways

Posted in: Highways


Imagine you could build a safer roadway with a few clicks of a button. You could evaluate a series of safety improvement alternatives along an existing highway and estimate the number of crashes and crash severity for each alternative – all from the comfort of your desk. Better yet, you are able to use the same data to develop benefit and cost ratios for each alternative to assist in selection of your improvements. This is just a portion of the capabilities that the Interactive Highway Safety Design Model  brings to modern projects as our industry strives to incorporate Performance-Based Practical Design practices.

The IHSDM is a suite of six modules that include Crash Prediction, Policy Review, Design Consistency, Intersection Review, Traffic Analysis and Drive/Vehicle created by the Federal Highway Administration.

The crash prediction module, in particular, is a valuable tool for engineers to analyze the safety of an existing highway or a series of proposed roadway improvement alternatives. Based on Part C of the 2010 Highway Safety Manual, the software uses the geometric design and traffic characteristics to estimate the frequency and severity of crashes of a given stretch of roadway.

Whether increasing the radius of a horizontal curve, flattening a vertical curve, widening a shoulder, or adding shoulder rumble strips, a designer can evaluate each of these treatments individually or in combination to develop cost-effective solutions to meet your project needs.

The Policy Review Module provides an initial assessment of the existing or proposed geometric design compared to current design standards. This module can also be used as a quality assurance check early in the design process to verify design standards are being met through the alternative development process. The remaining modules are referred to as the diagnostic evaluation modules and can be used to evaluate items such as:

  • operating speed consistency
  • traffic quality of service (mean speed or percent following on a corridor)
  • evaluation climbing/passing lane alternatives
  • intersection geometry
  • driver/vehicle performance

In March 2017, the Federal Highway Administration released the 12th version IHDSM. The recent update includes upgrades to the CPM and changes to the Policy Review module to incorporate FHWA revised controlling criteria.

I see the many applications and benefits of using IHSDM on projects. Do you see any shortcomings? Would you be open to experimenting with IHSDM on your next project?

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About the Author

Chris Rossmiller, PE recently completed training in the latest version of the IHSDM software. With 18 years of experience, he serves as project manager on a number of rural and urban improvement projects, working to improve roadway safety for both motorized and non-motorized users.

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