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The framework shown in Exhibit A-1 provides an outline of basic steps needed to evaluate an intersection and consider possible speed reduction treatments. 65 A P P E N D I X A Treatment Implementation Process Framework
66 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections INTERSECTION PRE-SCREENING Determine the need for intersection study Reports of high speeds, high crash frequency and/or severity, recurring crash types, and/or near misses Gather intersection data Speed Data 85 th -percentile speed Mean speed Speed variance Environment Rural/urban/suburban âOpenâ or âclosedâ cross section Building offsets Landscaping Visual complexity Pedestrians/bicycles Traffic Volume Composition User (commuter, recreational, tourist) Intersection Features Control type Sight distance Unconventional features Lane drops/merging Lighting Other geometric issues Crash Records Type Severity Intersection configuration Segment/intersection relationship Weather Time of day Assess Data Potential Scenarios Speeds are high, but no crashes occur: Is speed reduction needed? Speeds are high and crashes do occur: Will speed reduction reduce crashes? Speeds are appropriate, but crashes occur: Is additional speed reduction needed? Reason Speeds Are High Willful violation Inappropriate posted speed Environment contributes to speed (speed adaptation, lack of awareness, poor visibility) Congestion patterns Issues of High Speed Uniformity of flow Prevailing speeds above posted Role of Speed Is speed itself an issue? Where is speed an issue? Segment, transition, and intersection Exhibit A-1. Treatment implementation process framework.
Treatment Implementation Process Framework 67 TREATMENT SCREENING Fatal-Flaw Analysis Approach type Control type Physical constraints Cost Noise Maintenance Detailed Treatment Evaluation Target Speed Design Posted Operating Effects Speed effects Safety effects Maintenance Approach Type Major or minor Stop-controlled Signalized Uncontrolled Yield-controlled Type of Treatment Isolated Continuous Combination Potential Secondary Impacts Capacity Pedestrians/bicycles ADA Land use Economics Enforcement needs Construction TREATMENT IMPLEMENTATION Design Geometric and operational influence areas Opportunities to reinforce existing treatments/features Distance required for speed transition Perceptionâreaction distance Driver workload Opportunities to combine treatments Implementation Address public education and awareness Consider construction impacts Create evaluation plan Exhibit A-1. (Continued).
