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Suggested Citation:"Part II Contents." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/26394.
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Page 17
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Suggested Citation:"Part II Contents." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/26394.
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Suggested Citation:"Part II Contents." National Academies of Sciences, Engineering, and Medicine. 2021. Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/26394.
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Page 19

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17 Contents   SUMMARY ............................................................................................................................................... 20  CHAPTER 1 – CRASH PREDICTION MODEL OVERVIEW .......................................................... 21  1.1 Key Attributes ............................................................................................................................................. 21  1.2 Relationship to Current Highway Safety Manual .......................................................................................... 28  1.3 Local Calibration .......................................................................................................................................... 29  1.4 Future Highway Safety Manual Inclusion ..................................................................................................... 29  1.5 References .................................................................................................................................................. 30  CHAPTER 2 – DRAFT HIGHWAY SAFETY MANUAL TEXT ....................................................... 31  2.1 Overview ..................................................................................................................................................... 31  2.2 Introduction ................................................................................................................................................ 31  2.3 Overview of the Predictive Method ............................................................................................................. 32  2.4 Definitions and Predictive Model Overview ................................................................................................. 34  2.5. Predictive Method for Freeways with PTSU ................................................................................................ 36  2.6. Freeway Segments and Speed‐Change Lanes with PTSU .............................................................................. 51  2.7. Predictive Model for Freeway Segments with PTSU .................................................................................... 55  2.8. Predictive Model for Freeway Speed‐Change Lanes with PTSU .................................................................... 70  2.9. Supplemental Calculations to Apply SPF Adjustment Factors ...................................................................... 85  2.10. Calibration of the SPFs and SDFs to Local Conditions ................................................................................. 87  2.11. Limitations of Predictive Method .............................................................................................................. 89  2.12. Application of Predictive Method ............................................................................................................. 89  2.13. Summary .................................................................................................................................................. 90  2.14. References ............................................................................................................................................... 90  2.15. Sample Problems ...................................................................................................................................... 90  CHAPTER 3 – SPREADSHEET TOOL ............................................................................................ 107  3.1 Analysis Steps ........................................................................................................................................... 107  3.2 Getting Started .......................................................................................................................................... 108  3.3 Site Data Entry .......................................................................................................................................... 109  3.4 Results ...................................................................................................................................................... 113  3.5 References ................................................................................................................................................ 113  CHAPTER 4 – UNDERSTANDING RESULTS ............................................................................... 114  4.1 Performance Measures ............................................................................................................................. 114  4.2 Crash Frequency and Severity .................................................................................................................... 114  4.3 Comparison to Current Highway Safety Manual ......................................................................................... 115  4.4 References ................................................................................................................................................ 115 

18 List of Figures Figure 1. Illustrative sites for one‐directional freeway facility evaluation. ................................................................. 22  Figure 2. Example calculation of the length of transition zone within a site. .............................................................. 27  Figure 3. The HSM predictive method. ........................................................................................................................ 37  Figure 4. Through‐lane count in segments with a lane added or dropped. ................................................................ 44  Figure 5. Freeway speed‐change lane length. ............................................................................................................. 45  Figure 6. Measurement of cross section data elements. ............................................................................................ 46  Figure 7. Barrier variables. ........................................................................................................................................... 46  Figure 8. Distance to nearest ramp. ............................................................................................................................ 47  Figure 9. Clear zone width considerations. .................................................................................................................. 48  Figure 10. Determination of the length of transition zone within a site. .................................................................... 49  Figure 11. Determination of the length of turnout within a segment. ........................................................................ 50  Figure 12. Illustrative sites for one‐directional freeway facility evaluation. ............................................................... 51  Figure 13. Definition of freeway segments and speed‐change lane sites. .................................................................. 52  Figure 14. Segment boundaries based on PTSU lane presence. .................................................................................. 54  Figure 15. Segmentation for varying median width. ................................................................................................... 54  Figure 16. Graphical form of the SPFs for freeway segments. .................................................................................... 58  Figure 17. Graphical form of the SPFs for ramp entrance speed‐change lanes. ......................................................... 73  Figure 18. Graphical form of the SPFs for ramp exit speed‐change lanes. .................................................................. 74  Figure 19. Ramp access data for sample problem 1. ................................................................................................... 92  Figure 20. Plan view of speed‐change lane site evaluated for sample problem 2. ................................................... 101  Figure 21. Introduction worksheet. ........................................................................................................................... 109  Figure 22. Sample input of Segment worksheet. ....................................................................................................... 110  Figure 23. Sample summary results of Segment worksheet. .................................................................................... 110  Figure 24. Local calibration factors in LocalValues worksheet. ................................................................................. 111  Figure 25. Local severity distribution functions in LocalValues worksheet. .............................................................. 111  Figure 26. Local crash type distribution in LocalValues worksheet. .......................................................................... 112  Figure 27. Sample summary worksheet. ................................................................................................................... 113 

19 List of Tables Table 1. Adjustment factors in NCHRP Project 17‐89 FI crash prediction models. ..................................................... 24  Table 2. Adjustment factors in NCHRP Project 17‐89 PDO crash prediction models. ................................................. 25  Table 3. SPFs for urban freeways with PTSU. .............................................................................................................. 35  Table 4. SPFs for freeway segments. ........................................................................................................................... 56  Table 5. SPF adjustment factors for freeway segments. ............................................................................................. 56  Table 6. Applicable AADT volume ranges for freeway segment and speed‐change lanes. ......................................... 57  Table 7. SPF coefficients for freeway segments. ......................................................................................................... 58  Table 8. Coefficients for horizontal curve AF—freeway segments. ............................................................................. 59  Table 9. Coefficients for lane width AF—freeway segments. ...................................................................................... 59  Table 10. Coefficients for inside shoulder width AF—freeway segments. .................................................................. 60  Table 11. Coefficients for median width AF—freeway segments. .............................................................................. 61  Table 12. Coefficients for median barrier AF—freeway segments. ............................................................................. 62  Table 13. Coefficients for outside shoulder width AF—freeway segments. ............................................................... 63  Table 14. Coefficients for outside clearance AF—freeway segments. ........................................................................ 65  Table 15. Coefficients for outside barrier AF—freeway segments. ............................................................................. 65  Table 16. Coefficients for turnout presence AF—freeway segments. ......................................................................... 66  Table 17. Coefficients for PTSU operation AF—freeway segments. ............................................................................ 67  Table 18. Default distribution of crashes by crash type for freeway segments. ......................................................... 70  Table 19. SPFs for speed‐change lanes. ....................................................................................................................... 71  Table 20. SPF adjustment factors for speed‐change lanes. ......................................................................................... 71  Table 21. SPF coefficients for ramp entrance speed‐change lanes. ............................................................................ 72  Table 22. SPF coefficients for ramp exit speed‐change lanes. ..................................................................................... 74  Table 23. Coefficients for horizontal curve AF—speed‐change lanes. ........................................................................ 75  Table 24. Coefficients for lane width AF—speed‐change lanes. ................................................................................. 76  Table 25. Coefficients for inside shoulder width AF—speed‐change lanes. ................................................................ 76  Table 26. Coefficients for median width AF—speed‐change lanes. ............................................................................ 77  Table 27. Coefficients for median barrier AF—speed‐change lanes. .......................................................................... 78  Table 28. Coefficients for PTSU operation AF—speed‐change lanes. ......................................................................... 80  Table 29. Coefficients for ramp entrance length AF—speed‐change lanes. ............................................................... 80  Table 30. Coefficients for ramp exit length AF—speed‐change lanes. ........................................................................ 81  Table 31. Coefficients for severity distribution function—speed‐change lanes. ......................................................... 83  Table 32. Default distribution of crashes by crash type for speed‐change lanes. ....................................................... 84  Table 33. Crash frequency predictive models with a calibration factor. ..................................................................... 88  Table 34. Severity distribution functions with a calibration factor. ............................................................................ 88  Table 35. List of sample problems. .............................................................................................................................. 91 

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Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines Get This Book
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Left or right shoulders can be strategically opened as travel lanes, and "part-time shoulder use" is defined as using a shoulder "some, but not all, hours of the day.”

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 309: Safety Performance of Part-Time Shoulder Use on Freeways, Volume 1: Informational Guide and Safety Evaluation Guidelines provides an overview of part-time shoulder use, presents the results of past operational studies, and presents the results of safety research conducted through NCHRP's Safety Performance of Part-time Shoulder Use on Freeways project.

Supplemental to the document is a Freeway Analysis Tool, which includes BOS data, S D PTSU Data, and a Prediction Tool, as well as NCHRP Web-Only Document 309: Safety Performance of Part-Time Shoulder Use on Freeways, Volume 2: Conduct of Research Report.

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