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v Contents Summary ........................................................................................................................................ xi Chapter 1. Introduction ....................................................................................................................1 1.1 Introduction .........................................................................................................1 1.2 Research Objective and Scope ............................................................................2 1.3 Research Approach ..............................................................................................2 1.4 Organization of This Report ................................................................................3 Chapter 2. Literature and Current Practice Review .........................................................................4 2.1 Safety Effects of Geometric Design Features .....................................................4 2.2 Traffic Operational Effects of Geometric Design Features .................................5 2.3 Pavement Resurfacing Effects .............................................................................6 2.4 Cost-Effectiveness/Benefitâcost Tools ...............................................................6 2.5 Tort Liability Considerations ..............................................................................9 Chapter 3. Highway Agency Survey Results ................................................................................10 3.1 Survey Objectives ..............................................................................................10 3.2 Survey Response Rate and Type of Respondents .............................................10 3.3 Highway Agency 3R Design Policies and Criteria ...........................................11 3.4 Identification of the Need for 3R Projects .........................................................12 3.5 Consideration of Crash History in Design of 3R Projects .................................12 3.6 Inclusion of Safety Improvements in 3R Projects .............................................16 3.7 Crash Frequency and Severity Measures Used in 3R Project Analyses ...........18 3.8 Distinction Between Reconstruction and 3R Projects .......................................18 3.9 Use of the Practical Design Concept .................................................................23 3.10 Use of TRB Special Report 214 Design Guidelines .........................................25 3.11 Use of Analytical Tools in 3R Design Decisions ..............................................26 3.12 Need for Benefitâcost Analysis Tools ...............................................................26 Chapter 4. Current Highway Agency 3R Design Guidelines ........................................................28 4.1 3R Design Guidelines in TRB Special Report 214 ...........................................28 4.2 Highway Agency 3R Design Criteria Review ..................................................32 4.3 Evolving Design Approaches ............................................................................33 Chapter 5. Crash Reduction Effectiveness of Specific Design Improvement Types ....................34 5.1 Quantifying Crash Reduction Effectiveness of 3R Improvements: Crash Modification Factors ........................................................................................34 5.2 Crash Modification Factors for Specific 3R Improvement Types ....................38Â
vi Chapter 6. 3R Improvement Implementation Costs ......................................................................60 6.1 Lane Width ........................................................................................................60 6.2 Shoulder Width ..................................................................................................60 6.3 Paving an Existing Unpaved Shoulder ..............................................................61 6.4 Roadside Slope ..................................................................................................61 6.5 Superelevation Improvement/Restoration on Horizontal Curves .....................61 6.6 Rumble Strips ....................................................................................................61 6.7 Passing Lanes ....................................................................................................61 6.8 Median and Roadside Barriers on Freeways .....................................................62 6.9 Right-of-Way .....................................................................................................62 6.10 Incidental Costs .................................................................................................62 Chapter 7. Application of Benefitâcost Analysis for 3R Projects .................................................63 7.1 Elements of Benefitâcost Analysis ....................................................................63 7.2 Computational Examples of Benefitâcost Analysis ..........................................72 7.3 Interpreting Benefitâcost Analysis Results .......................................................77 7.4 Using Benefitâcost Analysis to Establish Minimum AADT Guidelines for 3R Improvements ....................................................................................................81 7.5 Specific Benefitâcost Analysis Applications for 3R Project Design Descriptions .......................................................................................................85 7.6 Alternative Approaches to Presenting Design Guidelines ................................87 7.7 Investing Available 3R Funds for Maximum Reduction of Crash Frequency and Severity .......................................................................................................90 Chapter 8. Spreadsheet Tools to Perform Benefitâcost Analysis for 3R Improvement Alternatives ..................................................................................................................94 8.1 Spreadsheet Tool 1âBenefitâcost Analysis for a Single Design Alternative .........................................................................................................94 8.2 Spreadsheet Tool 2âBenefitâcost Analysis for Comparison of Several Design Alternatives ..............................................................................96 Chapter 9. Development of Design Guidelines for 3R Projects ....................................................99 9.1 Overview ...........................................................................................................99 9.2 Scope of Guidelines .........................................................................................100 9.3 How Does the Design Process for 3R Projects Differ from the Design Process for New Construction and Reconstruction Projects? .........................101 9.4 Crash Reduction Effectiveness of 3R Improvements ......................................102 9.5 Benefitâcost Analysis Procedures ...................................................................103 9.6 Benefitâcost Analysis Tools ............................................................................103 9.7 3R Project Design Guidelines for Specific Roadway Types ...........................103 Chapter 10. Conclusions .....................................................................................................105 Chapter 11. References ........................................................................................................108
vii Appendices Appendix Aâ3R Project Implementation Cost Estimation Procedures Appendix BâSurvey Questionnaire Appendix CâUpdated Crash Cost Estimates Note: The contractorâs report published here is associated with NCHRP Research Report 876: Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Readers can read or purchase NCHRP Research Report 876 on the TRB website (www.TRB.org).
viii Figures Figure 1. Example of Safety Performance Function for Undivided Roadway Segments on Rural Multilane Highways ....................................................................37Â Figure 2. CMFra for Lane Width on Undivided Roadways on Rural Two-Lane Roadway Segments ......................................................................................................................39Â Figure 3. Crash Modification Factor for Shoulder Width on Rural Two-Lane Highway Roadway Segments ......................................................................................................41Â Figure 4. CMFra for Lane Width on Undivided Roadway Segments on Rural Multilane Highways .....................................................................................................................46Â Figure 5. CMFra for Lane Width on Divided Roadway Segments on Rural Multilane Highways .....................................................................................................49Â Tables Table 1. Summary of Safety Effects of Key Geometric Design Features ...................................5Â Table 2. Summary of Traffic Operational Effects of Key Geometric Design Elements .............6Â Table 3. Agency Types Represented by Survey Respondents ...................................................11Â Table 4. Agencies with Specific Geometric Design Policies or Criteria for 3R Projects ..........11Â Table 5. 3R Policies for NHS vs. non-NHS Projects and Federal Aid vs. State-Funded Projects .........................................................................................................................12Â Table 6. Identification of Need for 3R Projects .........................................................................12Â Table 7. Consideration of Crash History in 3R Projects ............................................................13Â Table 8. Methods to Consider Safety in Design Decisions for 3R Projects ..............................13Â Table 9. Assessment of How Often Safety Improvements Are Considered in 3R Projects ......16Â Table 10. Most Frequent Safety Improvements Included in 3R Projects ....................................17Â Table 11. Consideration of Pedestrians and Bicyclists in 3R Projects ........................................18Â Table 12. Crash Frequency Rate and/or Severity Measures Considered in 3R Project Analyses .......................................................................................................................18Â Table 13. Formal Definitions That Distinguish Between pReconstruction and 3R Projects .......19Â Table 14. Design Exception Process for Reconstruction and 3R Projects ...................................23Â Table 15. Use of the Practical Design Concept ...........................................................................24Â Table 16. Highway Agency Use of TRB Special Report 214 Design Guidelines for 3R Projects .........................................................................................................................25Â Table 17. Highway Agency Use of Analytical Tools in 3R Design Decisions ...........................26Â Table 18. Need for Benefitâcost Analysis Tool ...........................................................................27Â Table 19. Minimum Lane and Shoulder Widths for Rural Two-Lane Highways That Were Presented in TRB Special Report 214 .........................................................................28Â Table 20. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two- Lane Local Roads ........................................................................................................29Â Table 21. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two- Lane Collector Roads ...................................................................................................29Â Table 22. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two- Lane Arterial Roads .....................................................................................................30Â
ix Table 23. Usable Bridge Width Criteria for Bridge Replacement from TRB Special Report 214 ....................................................................................................................31Â Table 24. CMF for Lane Width on Rural Two-Lane Roadway Segments ..................................39Â Table 25. CMF for Shoulder Width on Rural Two-Lane Roadway Segments (CMFwra) ............40Â Table 26. CMFs for Shoulder Types and Shoulder Width on Roadway Segments (CMFtra) ......42Â Table 27. Roadside Slope CMFs for Rural Two-Lane Highways ...............................................44Â Table 28. CMFs for Installation of Left-Turn Lanes on Intersection Approaches ......................44Â Table 29. CMFs for Installation of Right-Turn Lanes on Intersection Approaches ....................44Â Table 30. CMF for Lane Width on Undivided Rural Multilane Roadway Segments ................45Â Table 31. Roadside Slope CMFs for Rural Multilane Highways ................................................48Â Table 32. CMFs for Installation of Left-Turn Lanes on Intersection Approaches ......................48Â Table 33. CMFs for Installation of Right-Turn Lanes on Intersection Approaches ....................48Â Table 34. CMF for Lane Width on Divided Rural Multilane Roadway Segment .......................49Â Table 35. CMFs for Paved Right (Outside) Shoulder Width on Rural Multilane Divided Highway Segments ......................................................................................................50Â Table 36. CMFs for Installation of Left-Turn Lanes on Intersection Approaches ......................51Â Table 37. CMFs for Installation of Right-Turn Lanes on Intersection Approaches ....................52Â Table 38. CMFs for Installation of Left-Turn Lanes on Intersection Approaches ......................53Â Table 39. CMFs for Installation of Right-Turn Lanes on Intersection Approaches ....................54Â Table 40. Coefficients for Inside Shoulder Width CMF on Freeways ........................................55Â Table 41. Coefficients for Outside Paved Shoulder Width CMF on Freeways ...........................55Â Table 42. Coefficients for Presence of Median Barrier CMF on Freeways ................................57Â Table 43. Coefficients for Presence of Outside Barrier CMF on Freeways ................................58Â Table 44. Coefficients for Median Width on Freeways ...............................................................59Â Table 45. Comprehensive Societal Costs of Crashes Updated from the Values Presented in the HSM ..................................................................................................69Â Table 46. Input Data for Safety Benefits Calculation Example ...................................................73Â Table 47. CMFs for Example Roadway Section..........................................................................73Â Table 48. Calculation of Annual Crash Reduction by Severity Level .........................................76Â Table 49. Example of Benefitâcost Calculations for Lane Widening from 10 to 12 ft in Level Terrain on a Rural Two-Lane Highway .........................................................79Â Table 50. Example of Benefitâcost Calculations for Lane Widening from 9 to 10 ft in Level Terrain on a Rural Two-Lane Highway .........................................................79Â Table 51. Example of Benefitâcost Calculations for Lane Widening from 9 to 11 ft in Level Terrain on a Rural Two-Lane Highway .........................................................80Â Table 52. Example of Benefitâcost Calculations for Lane Widening from 9 to 12 ft in Level Terrain on a Rural Two-Lane Highway .........................................................80Â Table 53. Example of Benefitâcost Calculations for Lane Widening from 10 to 11 ft in Level Terrain on a Rural Two-Lane Highway .........................................................80Â Table 54. Example of Benefitâcost Calculations for Lane Widening from 11 to 12 ft in Level Terrain on a Rural Two-Lane Highway .........................................................81Â Table 55. Example of Incremental Analysis to Determine Net Benefits of Lane Widening for Existing Rural Two-Lane Highways with 9-ft Lanes in Level Terrain .................82Â Table 56. Examples of Incremental Analysis to Determine Net Benefits of Lane Widening for Existing Rural Two-Lane Highways with 10-ft Lanes in Level Terrain ...............84Â
x Table 57. Example of AADT Levels at which Lane Widening Becomes Cost-Effective| Rural Two-Lane Highway Segments Assuming 2-ft Paved Shoulders, 1V:3H Roadside Foreslopes, and Moderate Horizontal Curvature .........................................86Â Table 58. Example of AADT Levels at which Shoulder Widening Becomes Cost-Effective Rural Two-Lane Highway Segments Assuming 10-ft Lanes, Paved Shoulders, 1V:3H Roadside Foreslopes, and Moderate Horizontal Curvature .............................86