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v TABLE OF CONTENTS 1 BACKGROUND ................................................................................................................... 1 2 APPLICABILITY ................................................................................................................. 3 3 PROCEDURE ....................................................................................................................... 3 3.1 Roadside Hardware Replacement Analysis Workbook ................................................... 5 3.2 Risk Assessments for Existing Hardware ........................................................................ 7 3.2.1 Step 1: Number of Years of Available Crash Data ................................................... 7 3.2.2 Step 2: Total Number of Crashes with Existing Hardware....................................... 7 3.2.3 Step 3: Number of Fatal and Serious Injury Crashes with Existing Hardware ........ 8 3.2.4 Step 4: Confidence Level .......................................................................................... 8 3.2.5 Step 5: Mean Risk and Confidence Interval ............................................................. 9 3.2.6 Step 6: Quantity of Existing Hardware in the Crash Reporting Area ..................... 10 3.2.7 Step 7: Hardware Traffic Exposure ........................................................................ 11 3.2.8 Step 8: Police-Reported Crash Rate ........................................................................ 11 3.3 Relative Risk Estimates for Replacement Hardware ..................................................... 12 3.3.1 Step 9: Estimate Fatal and Serious Injury Crash Risk for Replacement Hardware 12 3.3.2 Step 10: Statistical Significance.............................................................................. 12 3.3.3 Step 11: Relative Risk Reduction ........................................................................... 12 3.4 Project Details ................................................................................................................ 12 3.4.1 Step 12: Design Year Traffic Volume .................................................................... 12 3.4.2 Step 13: Quantity of Replacement Hardware ......................................................... 13 3.4.3 Step 14: Unit Installed Cost of Replacement Hardware ......................................... 13 3.4.4 Step 15: Unit Cost of Hardware Removal .............................................................. 13 3.4.5 Step 16: Total Cost of Each Type of Replacement Hardware ................................ 13 3.5 Economic Analysis ......................................................................................................... 14 3.5.1 Step 17: Annual Number of Fatal and Serious Injury Crashes Avoided ................ 14 3.5.2 Step 18: Total Cost of Replacement Hardware ....................................................... 14 3.5.3 Step 19: Value of Statistical Life ............................................................................ 14 3.5.4 Step 20: Annual Societal Benefit of Crashes Avoided ........................................... 15 3.5.5 Step 21: Design Life ............................................................................................... 15 3.5.6 Step 22: Internal Rate of Return ............................................................................. 15 3.6 Interpreting Results ........................................................................................................ 16 4 EXAMPLE........................................................................................................................... 16 4.1 Replacing Strong Post W-Beam Guardrail .................................................................... 16 4.1.1 Steps 1â8: Risk Assessment of Existing Guardrails ............................................... 17 4.1.2 Steps 9â11: Relative Risk Estimates for Replacement Guardrail ........................... 17 4.1.3 Steps 12â17: Project Details for Guardrails ............................................................ 18 4.2 Replacing Report 350 Terminals with MASH 2016 Terminals ..................................... 18 4.2.1 Steps 1â8: Risk Assessment of Existing Terminals ................................................ 18 4.2.2 Steps 9â11: Relative Risk Assessment of Replacement Terminals ........................ 19 4.2.3 Steps 12â17: Project Details for Terminals ............................................................ 19 4.3 Economic Analysis ......................................................................................................... 19 4.4 Discussion ...................................................................................................................... 20 5 REFERENCES .................................................................................................................... 22
vi LIST OF FIGURES Figure 1. Roadside Hardware Replacement Analysis Workbook. ................................................. 6 Figure 2. Worksheet for Considering the Replacement of 27-inch W-Beam Guardrail with 31-inch W-Beam Guardrail and Associated Terminals. .................................... 21 LIST OF TABLES Table 1. Roadside Hardware Replacement Analysis Steps. ........................................................... 4 Table 2. Typical Mean Risk Values for Select Roadside Hardware. .............................................. 9 Table 3. Common Confidence Levels and Z Scores..................................................................... 10
vii ACRONYMS AASHTO American Association of State Highway and Transportation Officials FHWA Federal Highway Administration MASH Manual for Assessing Safety Hardware MMUCC Model Minimum Uniform Crash Criteria NOMENCLATURE AADT Average daily traffic in vehicles/day. AADTo The measured average annual daily traffic in vehicles/day. ABCA Annual benefit of fatal and serious injury crashes avoided in dollars. CL Confidence level. CREHJ Police-reported crash rate for existing hardware type j in units of crashes/MVMP for continuous roadside hardware or crashes/MVP for discreet roadside hardware. CRHJ Cost of replacing hardware type j in dollars. EEHJ Existing hardware type j exposure in units of MVMP for continuous roadside hardware or MVP for discreet roadside hardware. FCSAJ Annual number of fatal and serious injury crashes avoided. G Traffic volume growth as a decimal. IIR Internal rate of return as a percent. m Number of types of hardware considered for replacement. MVMP Million vehicle miles passing continuous hardware type j. MVP Million vehicles passing discreet hardware type j. NCj Number of crashes of all severity involving hardware type j. NFSCj Number of fatal and serious injury crashes involving hardware type j. QEHJ Quantity of existing hardware type j in the same area used for collecting crash data in ft for continuous hardware and each for discreet hardware. QEHJ Quantity of existing hardware type j in ft for continuous hardware and each for discreet hardware. REHJ Fatal and serious injury crash risk for existing hardware type j. RRHJ Fatal and serious injury crash risk for replacement hardware type j. RRRJ Relative risk reduction for replacing existing hardware type j with upgraded hardware. TCRH Total hardware replacement cost in dollars. UCIHJ Unit cost of installing replacement hardware type j in dollars. UCRHJ Unit cost of removing existing hardware type j in dollars. VSL Value of statistical life in dollars. YCD Years of available police-reported crash data. YD Number of years between the observed AADT and the design year in years. YL Project life in years.