Sideslope CMF for 4 Lane Rural Roadways

Safety performance functions, development (calibration, crash modification factors [Part C], crash proportions), IHSDM and other software

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Sideslope CMF for 4 Lane Rural Roadways

Postby dengstro » Fri Apr 26, 2013 2:07 pm

If barrier (guardrail) is present on the right side of a multilane rural roadway, does this negate the sideslope CMF? What should be used?
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Re: Sideslope CMF for 4 Lane Rural Roadways

Postby mdimaiuta » Tue May 07, 2013 2:07 pm

The presence of barrier (guardrail) does not negate the sideslope CMF. A current limitation of the HSM Part C methods is that they do not consider guardrail. In addition, HSM Part D does not contain CMFs related to guardrail. Section 13A.3.2.5 (P. 13-64) "Install Roadside Barrier along Embankment" states, "Installing roadside barriers along embankments appears to reduce the number of fatal and injury run-off-the-road crashes and the number of run-off-the-road crashes of all severities. However, the magnitude of the crash effect is not certain at this time. It is expected that the crash effect of installing roadside barriers is related to existing roadside features and roadside geometry."

I also searched the CMF Clearinghouse (http://www.cmfclearinghouse.org) for CMFs related to barriers/guardrail, but did not find anything directly applicable to your situation.

The good news... NCHRP Project 17-54 "Consideration of Roadside Features in the Highway Safety Manual" (http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=2979) is an active project with an objective "to develop quantitative measures that can be incorporated into the HSM to evaluate the effects of roadside designs and features on the frequency and severity of lane departure crashes." The Project website currently shows a completion date of July 2014. Results of this research will greatly enhance the capabilities of HSM Part C methods to consider the effects of various roadside features.

Mike Dimaiuta
IHSDM / HSM Support
ihsdm.support@dot.gov
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