Calibrating the HSM Predictive Methods for Oregon Highways

AASHTO, FHWA, and TRB have combined efforts to develop a document similar to the Highway Capacity Manual known as the Highway Safety Manual (HSM). This publication will be published by AASHTO and is expected to be used as a supporting document in the design and assessment of highway facilities in the United States. The manual is targeted for release in 2010; however, there may be a NCHRP Synthesis released in 2009 so that agencies can see the recommended procedures and know how to prepare for these changes in safety assessment. The first edition of the HSM will include a section…

AASHTO, FHWA, and TRB have combined efforts to develop a document similar to the Highway Capacity Manual known as the Highway Safety Manual (HSM).  This publication will be published by AASHTO and is expected to be used as a supporting document in the design and assessment of highway facilities in the United States.  The manual is targeted for release in 2010; however, there may be a NCHRP Synthesis released in 2009 so that agencies can see the recommended procedures and know how to prepare for these changes in safety assessment.  The first edition of the HSM will include a section known as “Predictive Methods” that will provide science-based analytical procedures for estimating the safety of a road and how modifying certain road characteristics will influence the safety of a facility.  The models and adjustment factors were developed from various data sets and it is emphasized in this document the importance of calibrating safety performance functions to specific local conditions.  Without calibration of the predictive procedures for local conditions, the HSM methods can provide misleading recommendations that could result in inappropriate investment of safety funds. The calibration effort is generally viewed by most practioners as time consuming and complicated. Moreover, the calibration exercise is efficiently accomplished using a statewide approach and for all models simultaneously.  Both Karen Dixon and Chris Monsere serve as members of the TRB Task Force for the Development of the Highway Safety Manual.  In fact, Karen Dixon chairs the research sub-committee for this TRB effort.  As a result, Oregon researchers already have full access to the procedures that will be included in the HSM and can initiate calibration of these procedures for the State of Oregon so that Oregon transportation agencies will be prepared to use the document to its fullest potential upon release. 

The HSM includes predictive methods for:
• Rural, two lane roads;
• Rural, multilane highways; and
• Urban and suburban arterial highways.

Each of these predictive methods is based on unique assumptions or crash trends that may or may not be applicable for Oregon rural highways or urban streets.  This proposed research effort will use local conditions (crash data, road geometry information, and traffic volume data) to calibrate the HSM predictive procedures for Oregon facilities.

The greatest benefit of this research effort is that the transportation agencies in Oregon will be ready to use the predictive methods in the HSM and have in place calibration procedures for the use of this document upon its release.  This will enable accurate results and insure appropriate safety investment decisions based on the HSM predictive procedures.  AASHTO will be the agency ultimately responsible for the publication of this document and it is expected that the HSM will serve as a companion document to the AASHTO Green Book and the AASHTO Roadside Design Guide for the safe design of roads in the United States. As a result, it is likely that the HSM will quickly become a standard in the United States.