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Gain insight into crash patterns and causes to select effective countermeasures at candidate sites. Review crash statistics, assess field conditions, and identify safety concerns. Use the Haddon Matrix to select countermeasures. Perform economic appraisal and prioritize projects using benefit-cost analysis and optimization methods. Evaluate safety effectiveness through observational before-after studies.
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DIAGNOSIS • Objective • to gain an understanding of crash patterns and causes so that potential countermeasures can be selected at the candidate sites • Steps • Safety data review: crash statistics, collision diagrams, • Assess supporting documentation • Assess field conditions • Identify safety concerns
SELECT COUNTERMEASURES • Objective • Select countermeasures that can effectively reduce the crashes identified in DIAGNOSIS • Steps • Identify contributing factors • Haddon Matrix • Select countermeasures
HADDON MATRIX Example Haddon Matrix for Rear-end Crash
CRASHES AT SIGNALIZED INTERSECTIONS • Angle crashes • Rear-end or sideswipe • Left- or right-turn • Nighttime • Wet pavement • Pedestrian/bicyclist
ECONOMIC APPRAISAL • Benefit-cost analysis • Change in crash • Convert benefits to $ • Estimate project costs • Benefit/cost ratio • Non-monetary considerations
ANNUAL BENEFITS TO PRESENT VALUE Example: What is the benefit cost ratio for a countermeasure implementation that will cost $3,000,000, but with an annual benefit of $872,400? Assume service life is 5 years and a rate of return of 4%.
PRIORITIZE PROJECTS • Project prioritization • Ranking by economic effectiveness measures • Incremental benefit-cost analysis • Optimization methods
SAFETY EFFECTIVENESS EVALUATION • Evaluation of the actualeffectiveness • Observational Before-afterstudies