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Unformatted text preview: The Pennsylvania State University Department of Civil and Environmental Engineering CE 321: Highway Engineering Class # 38: Traffic Signal Timing Spring 2008 Signal Timing Procedure (Steps) 1. Determine Phasing 2. Establish Analysis Lane Groups 3. Calculate Analysis Flow Rates and Adjusted Saturation Flow Rates 4. Determine Critical Lane Groups and Total Cycle Lost Time 5. Calculate Cycle Length 6. Allocate Green Time 7. Calculate Change and Clearance Intervals 8. Check Pedestrian Crossing Time 9. Determine Level of Service Step 1: Determine phase to use Minimum # of phases (two): 1 2 Three phases: 2 3 1 Step 1: Determine phasing to use Add Protected Left Turn phase if: LT x Opposing Traffic > 50,000 during peakhour for one opposing lane; LT x Opposing Traffic > 90,000 for 2 opposing lanes LT x Opposing Traffic > 110,000 for 3 opposing lanes Lead / Lag Phasing: LT precede right and throughmovements in phase is leading. LT follows right and throughmovements in phase is lagging. Step 1: Determine phase to use Minimum # of phases (two): 1 2 Three phases: 2 3 1 (Y +AR) 1 (Y + AR) 2 (Y + AR) 3 Step 2: Establish Lane Groups Treat each intersection approach separately. Based on lane and traffic movements: Simultaneous movements made from same lane must be treated as lane group. Treat exclusive turn lane as separate lane group. If approach includes exclusive turn lane, remaining lanes considered as single lane group. Step 2: Establish Lane Groups Step 3: Analysis Flow Rates and Saturation Flow Rates Convert hourly traffic volumes on each approach to analysis flow rates Divide volume by PHF. Use PHF for intersection. Saturation flow rate = s = 3600/h Step 4: Determine Critical Lane Groups and Total Cycle Lost Time Critical lane group is the one during a phase that controls green time for that phase. Use flow ratios = = n i ci c s v Y 1 Y c = sum of flow ratios for critical lane groups (v/s) ci = flow ratio for critical lane group i n = number of critical lane groups Step 4: Determine Critical Lane Groups and Total Cycle Lost Time Apply lost time for critical lane group when its movements are initiated....
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 Spring '02
 Petrucha
 Environmental Engineering

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