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Preface to the Highway Safety Manual Supplement

Throughout the development of the first edition of the Highway Safety Manual, the researchers and practitioners involved in the process recognized that all of the material desired for the HSM would not be ready for publication in the first edition in 2010. Even before the first edition was on press, research had begun to develop additional materials for eventual inclusion in later editions of the HSM.

This supplement to the HSM contains two chapters presenting predictive models for freeway and interchange facilities, similar to the models contained in Part C of the first edition. These chapters are published as a supplement to allow users access to these materials prior to publication of the next edition. As with the full first edition of the HSM, these chapters have been formally approved by the AASHTO committees and subcommittees involved in the development as well as the Board of Directors. The considerations and cautions discussed in the Preface of the first edition also apply to this supplement.

Under National Cooperative Highway Research Program Project 17-45, the Texas A&M Transportation Institute (James A. Bonneson, Principal Investigator) performed research to develop the models and information in this supplement and prepared the text of these chapters. The volunteers of the AASHTO Subcommittee on Safety Management Task Group on Technical Safety Publication Oversight and Outreach and of the Transportation Research Board Highway Safety Performance Committee, supported by members of the AASHTO Subcommittees on Design and Traffic Engineering, contributed their technical expertise and input to the NCHRP panel to help ensure the materials meet the needs of the researchers and practitioners who use the HSM.