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LOW COST SAFETY IMPROVEMENTS

LOW COST SAFETY IMPROVEMENTS. The Tools – Traffic Signals – Session #8. Traffic Signals. Learning Outcomes: Identify countermeasures for operation and design deficiencies of traffic signals. Traffic Signals. New Tools:.

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LOW COST SAFETY IMPROVEMENTS

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  1. LOW COST SAFETY IMPROVEMENTS The Tools – Traffic Signals – Session #8

  2. Traffic Signals Learning Outcomes: • Identify countermeasures for operation and design deficiencies of traffic signals

  3. Traffic Signals • New Tools: NCHRP 440 – Accident Mitigation Guide for Congested Rural Two-Lane Highways NCHRP 500 – Volume 5: A Guide for Addressing Unsignalized Intersection Collisions

  4. Traffic Signals • New & Proven Technologies

  5. Traffic Signals • How can Traffic Signals Reduce crashes? • Which Signal Configurations, Equipment, and Operations Reduce Crashes? • What is the Safety Effect of each? Discussion

  6. Safety Benefits of Traffic Signals • Install new Traffic Signal – All Crashes (CTRE 00-61, 2001) CRF=27% Tried • Install new Traffic Signal CRF=7% 3 Approaches 4 Approaches Tried Increase Crashes 2% • Upgrade Traffic Signal (Fatalities) (Injuries) 38% 22% Proven

  7. Safety Benefits of Traffic Signals Tried Change type of Traffic Control (3 and 4 approach Unsignalized to Signal Control) CRF = 60% Table 13.3: AMFs for Urban-Intersection Signalization (Injury-related crashes ONLY)(Persaud et al., 2002)

  8. Is this traffic signal as safe as it could be? • What are some Traffic Signal Features/Equipment that affect Safety? • Let’s list them Discussion

  9. Traffic Signals Countermeasures 1. Update yellow Clearance timing 2. Add All-Red Clearance phase 3. Improve visibility (12” sections, suppl. heads, etc) 4. Add Back Plates 5. Change Permissive Lefts to Protected Only

  10. Traffic Signals Countermeasures 6. Add Advance Warning signs with active flashers 7. Add Supplemental Signal Heads 8. Use Overhead Red “T” Heads 9. Change Late Night Yellow/Red Flash to Full Time Signal 10. Coordination of Signals 11. Controller/Actuation Upgrades

  11. Frequency of Red Light Running: *TTI, Bonneson, 2003

  12. Engineering Countermeasures to Red-Light Running: Tried *TTI, Bonneson, 2003

  13. Update Clearance Intervals ITE Traffic Engineering Handbook Proven Yellow Time All-Red Time *NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals

  14. Update Clearance Intervals Yellow Time Red Time ITE Traffic Engineering Handbook CP = t + V/2a + V/20*64.4*g + (W+L)/V • For 85th percentile approach speed of 45 mph, curb radius (Stop bar to curb line of intersecting street of 50’, And Intersection width of 36 feet Yellow Time = t + V/2a + V/20*64.4*g = 1.0 + 45*88/60/2*10 + 45*88/60/20*64.4*0% = 1.0 +66/20 = 1.0 + 3.3 = 4.3 seconds

  15. Update Clearance Intervals *TTI, Bonneson, 2003

  16. Update Clearance Intervals • reduces RLR frequency by 50-70% • reduces RLR crashes by 25% • reduces RLR frequency by 50-70% • CRF = 4 to 31% Total Crashes • CRF = 1 to 30% Right Angle Crashes *TTI, Bonneson, 2003

  17. Update Clearance Intervals * From ITE Traffic Signal Handbook Proven *NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals

  18. Add All-Red Clearance Interval ITE Traffic Engineering Handbook – All-Red Clearance Interval Tried T = ( W + L) / V CRF=25% for Add 1.0 Sec All-Red *Bhesania, 1991 Example: 85th Speed=45mph, W=36, curb radius=50’, L=20’ Red Time = (W+L)/V = (50 + 36 + 20)/45*88/60 = 106/66 = 1.61seconds

  19. Improve Visibility (12” Indications, Suppl heads) Tried Mast Arm Signals * Iowa CRF = 32% Related Crashes 8” to 12” Indications, *Winston-Salem, NC * Bonneson CRF = 24% All Crashes 33-47% Right Angle Crashes

  20. Treatment Finding Replace pedestals with mast arms (166) 49% estimated reduction in all crashes. 44% estimated reduction in fatal/injury 51% estimated reduction in property damage only (PDO) collisions. 74% estimated reduction in right angle collisions. 41% estimated reduction in rear end 12% estimated reduction in left-turn Improve Visibility (Mast Arms) Tried

  21. Improve Visibility – Signal Head per Lane) 1 head for 1 Lt lane 4 heads for 4 lanes Tried 1 head for 1 Rt lane CRF = 10 - 22%, Total Crashes, *ICBC, Winston-Salem, NC CRF = 47%, Right Angle Crashes

  22. Treatment Finding Add a signal head(135) 15% estimated increase in all collisions. 47% estimated reduction in right angle collisions. Add a primary signal head (168) 10% to 25% estimated reduction in fatal/injury 30% to 35% estimated reduction in property-damage-only collisions. 15% to 45% estimated reduction in right-angle 0% to 45% estimated reduction in rear-end Improve Visibility (Add a Signal Head) Tried

  23. Improve Visibility (Supplemental Signal Head) Tried Supplemental Signal Head CRF = 15%, Total Crashes, *ICBC, Winston-Salem, NC CRF = 47-48%, Right Angle Crashes

  24. Add Back Plates Tried CRF= 32% Right angle crashes, CRF= 2% to 24% All Crashes No Back Plates Back Plates

  25. Add Back Plates Tried -50% reduction in RLR * Bonneson CRF= 2% - 24%

  26. Retroreflectorize Back Plates Canadian retro- reflectorized backplate CRF=32% reduction in RLR Crashes CRF = 12% increase in all crashes Tried

  27. Retroreflectorize Back Plates Canadian retro- reflectorized backplate 32% Reduction in RLR Related Crashes Tried

  28. Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY • “T” Intersection • 3 Thru Lanes Westbound with ADT of 34,000; Side Street ADT is 1,400 NY 44 Westbound

  29. Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY • What low cost safety countermeaures would you consider? • What is the safety effect (CRF) for each? Discussion

  30. Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY Relevant Countermeasures: • Change 8” to 12” Indications • Add Backplates • Add All-Red Phase • Revise Change Interval • Remove Sight Obstruction of Parked Vehicles on Southeast Quadrant NY 44 Westbound

  31. Left Turn Lanes + Left Turn Phases Add a Left Turn Phase to Existing Signal CRF = 23% to 48% Total Crashes Tried CRF = 63% to 70% Left Turn Crashes *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation

  32. Left Turn Lanes + Left Turn Phases Add a Protected/Permissive Left Turn Phase to Existing Signal Tried CRF = 4% to 10% Total Crashes CRF = 40% to 64% Left Turn Crashes *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation

  33. Left Turn Lanes + Left Turn Phases Add a Left Turn Phase + Left Turn Lane to Existing Signal Tried CRF = 35% Total Crashes CRF = 58% (Iowa), Left Turn Crashes *NCHRP 500, Objective 17.2 A1 – Employ Left Turn Signal Phase

  34. Left Turn Lanes + Left Turn Phases Signalize and Add a Left Turn Lane without Left Turn Phase Tried CRF = 21% to 25% Total Crashes CRF = 46% to 54% Left Turn Crashes CRF = 15% Total Crashes *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation

  35. Left Turn Lanes + Left Turn Phases Signalize and Add a Left Turn Lane + Left Turn Phase Tried CRF=25% to 36% Total Crashes 58% Reduction in Crashes, *Iowa CRF=43% to 45%, Left Turn Crashes *NCHRP 500, Objective 17.2 A1 – Provide Left Turn Signal Phase

  36. Change Permissive Left to Protected Left Only CRF = 97% to 98% Left Turning Crashes *NCHRP 500, Objective 17.2 A1 – Provide Protected Left Turn Signal Phase Proven * Winston-Salem, NC

  37. Add Signal Ahead Advance Warning Sign Tried CRF= 35-40% • Winston-Salem, NC • McGee • MN DOT

  38. Treatment Finding Post SIGNAL AHEAD warning signs—urban(98) 16%-35% estimated decrease in all collisions. Post SIGNAL AHEAD warning signs—rural(98) 16%-40% estimated decrease in all collisions. Post SIGNAL AHEAD signs(135) 44% estimated decrease in right-angle collisions. Advance-warning flasher (172) 44% decrease in all fatal/injury 53% decrease in pd crashes 73% decrease in all fat/inj-angle crashes. 82% increase in all rear-end fatal-injury Add Signal Ahead Advance Warning Sign Tried

  39. Add Advance Warning Sign with Active Flashers tied to Signal Operation Tried CRF=35% to 67% Reduction in RLR Related Crashes, *Bonneson

  40. Treatment Finding Post SIGNAL AHEAD warning signs—urban(98) 16%-35% estimated decrease in all collisions. Post SIGNAL AHEAD warning signs—rural(98) 16%-40% estimated decrease in all collisions. Post SIGNAL AHEAD signs(135) 44% estimated decrease in right-angle collisions. Advance-warning flasher (172) 44% decrease in all fatal/injury collisions. 53% decrease in property-damage-only 73% decrease in all fatal/injury-angle 67% decrease in all fatal/injury left-turn 82% estimated increase in all rear-end Add Advance Warning Signs & Flashers Tried

  41. Add Supplemental Signal Head(s) Supplemental Far Left Signal Head

  42. Add Supplemental Signal Head(s) • Crest Vertical Curve + Right Hand Curve • Sight Distance is Limited By Noise Walls

  43. Overhead Red “T” Signal Heads Tried CRF = 12% total crashes CRF = 33% Reduction in Rt angle crashes, *Winston-Salem, NC

  44. Flashing Operation Issue BenefitDetriment • Yellow on mainline/Red on side street - if volume ratio is three or more • Yellow on mainline/Red on side street – if volume ratio is less than three or if adequate sight distance is not available

  45. Flashing Operation • Change late night flash of Yellow on mainline/Red on side street to normal operating traffic signal mode Tried CRF = 29% Total Crashes CRF = 80% Right Angle Crashes *Winston-Salem, NC

  46. Signal Coordination Proven CRF = 15% to 17% total crashes – 5 studies CRF = 25% to 38% Right Angle Crashes *NCHRP 500, Objective 17.2 A4 – Employ Signal Coordination

  47. Traffic Signals *NCHRP 500, Objective 17.2 E-3 – Implement Automated Enforcement of Red-Light Running Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red Light Running Proven Available thru ITE ITE website: www.ite.org

  48. Traffic Signals Review Question: What is the Recommended Practice re Calculation of Change Intervals? ITE Traffic Engineering Handbook CP = t + V/2a + V/20*64.4*g + (W+L)/V • reduces RLR frequency by 50-70% • CRF = 4 to 31% Total Crashes • CRF = 1 to 30% Right Angle Crashes

  49. Traffic Signals Learning Outcomes: • Identify countermeasures for operation and design deficiencies of traffic signals

  50. Traffic Signals Questions?

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