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20 P A R T - T I M E S H O U L D E R U S E S A F E T Y E V A L U A T I O N G U I D E L I N E S Summary One of the objectives of National Cooperative Highway Research Program (NCHRP) Project 17-89, Safety Performance of Part-time Shoulder Use on Freeways, was to âdevelop quantitative tools for practitioners to use to evaluate safety performance of freeways with part-time shoulder use as a function of temporal, operational, and other conditions when the shoulder is open or closed to traffic.â To address this objective, crash prediction models for freeways with part-time shoulder use (PTSU), suitable for inclusion in a future edition of AASHTOâs Highway Safety Manual (HSM), were developed. This document presents (1) an overview of the crash prediction models, (2) draft text for a future edition of the HSM, (3) information on a spreadsheet tool that implements the crash prediction models, and (4) a discussion of understanding results from the crash prediction model. A separate document, the PTSU Informational Guide, discusses findings obtained from models, such as the magnitude of crash frequency changes associated with the implementation of PTSU on freeways.
