Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines (2021)

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14  Inside shoulder width  Median width  Horizonal curve  Clear zone width  PTSU lane presence Section 2.6.2 of the draft HSM text in the PTSU Safety Evaluation Guidelines provide specific distances that represent a change in cross-sectional measurements and thus a need to begin a new segment. In practice, the start and end of speed-change lanes, horizontal curves, and PTSU lanes will form the boundaries of the majority of segments on most facilities. Alternative Analysis The CPMs developed for NCHRP 17-89 include a large number of variables. Alternatives that change any of these variables may be evaluated by predicting crash frequencies multiple times and comparing results. It is likely that many users will use these CMPs to evaluate the potential installation of a PTSU facility on an existing freeway, and the CPMs are well-suited for doing this. Other potential uses include the following:  Comparison to multiple PTSU alternatives, such as different cross-sectional geometries  Predictive safety analysis of a freeway with an existing PTSU facility  Predictive safety analysis of one direction of an urban freeway for any reason  Safety network screening, as described in Part B of the HSM.  Safety benefit-cost analysis Analysis Tool A spreadsheet tool that implements the crash prediction models was developed through NCHRP Project 17-89. The spreadsheet tool computes the predicted crash frequency and severity of freeway sites with or without PTSU. If users provide historical crash data for an existing freeway, the spreadsheet tool computes expected crash frequency. Additional information and instructions for use of the spreadsheet tool is provided in Chapter 3 of the PTSU Safety Evaluation Guidelines. Figure 71. NCHRP Project 17-89 spreadsheet tool with sample data.