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

8-2 Traffic Signals Learning Outcomes: 1.Identify countermeasures for operation and design deficiencies of traffic signals

8-3 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

8-4 New & Proven Technologies Traffic Signals

8-5 Traffic Signals  How can Traffic Signals Reduce crashes?  Which Signal Configurations, Equipment, and Operations Reduce Crashes?  What is the Safety Effect of each? Discussion

8-6 Safety Benefits of Traffic Signals  Install new Traffic Signal  Upgrade Traffic Signal (Fatalities) (Injuries) CRF=7% 38% 22%  Install new Traffic Signal – All Crashes (CTRE 00-61, 2001) CRF=27% Proven Tried 3 Approaches 4 Approaches Tried Increase Crashes 2%

8-7 Safety Benefits of Traffic Signals Change type of Traffic Control (3 and 4 approach Unsignalized to Signal Control) Tried CRF = 60% Table 13.3: AMFs for Urban-Intersection Signalization (Injury-related crashes ONLY) (Persaud et al., 2002)

8-8 Is this traffic signal as safe as it could be? Discussion  What are some Traffic Signal Features/Equipme nt that affect Safety?  Let’s list them

8-9 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

8-10 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

8-11 Frequency of Red Light Running: *TTI, Bonneson, 2003

8-12 Engineering Countermeasures to Red-Light Running: *TTI, Bonneson, 2003 Tried

8-13 Update Clearance Intervals All-Red Time Yellow Time ITE Traffic Engineering Handbook *NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals Proven

8-14 Update Clearance Intervals Red Time Yellow Time ITE Traffic Engineering Handbook CP = t + V/2a + V/20*64.4*g + (W+L)/V  For 85 th percentile approach speed of 45 mph, curb radius (Stop bar to curb line of intersecting street of 50’, And Intersection width of 36 feet = t + V/2a + V/20*64.4*g = *88/60/2* *88/60/20*64.4*0% = /20 = = 4.3 seconds Yellow Time

8-15 Update Clearance Intervals *TTI, Bonneson, 2003

8-16 Update Clearance Intervals *TTI, Bonneson, reduces RLR frequency by 50-70% - reduces RLR crashes by 25% -reduces RLR frequency by % CRF = 4 to 31% Total Crashes CRF = 1 to 30% Right Angle Crashes

8-17 Update Clearance Intervals * From ITE Traffic Signal Handbook Proven *NCHRP 500, Objective 17.2 A2 – Optimize Clearance Intervals

8-18 Add All-Red Clearance Interval ITE Traffic Engineering Handbook – All-Red Clearance Interval T = ( W + L) / V Example: 85 th Speed=45mph, W=36, curb radius=50’, L=20’ Red Time = (W+L)/V = ( )/45*88/60 = 106/66 = 1.61seconds CRF=25% for Add 1.0 Sec All-Red *Bhesania, 1991 Tried

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

8-20 Improve Visibility (Mast Arms) Tried TreatmentFinding 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

8-21 Improve Visibility – Signal Head per Lane) Tried CRF = %, Total Crashes, *ICBC, Winston-Salem, NC CRF = 47%, Right Angle Crashes 1 head for 1 Lt lane 4 heads for 4 lanes 1 head for 1 Rt lane

8-22 Improve Visibility (Add a Signal Head) Tried TreatmentFinding 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

8-23 Improve Visibility (Supplemental Signal Head) Supplemental Signal Head CRF = 15%, Total Crashes, *ICBC, Winston- Salem, NC Tried CRF = %, Right Angle Crashes

8-24 Add Back Plates No Back PlatesBack Plates Tried CRF= 32% Right angle crashes, CRF= 2% to 24% All Crashes

8-25 Add Back Plates -50% reduction in RLR * Bonneson Tried CRF= 2% - 24%

8-26 Retroreflectorize Back Plates Canadian retro- reflectorized backplate CRF=32% reduction in RLR Crashes Tried CRF = 12% increase in all crashes

8-27 Retroreflectorize Back Plates Canadian retro- reflectorized backplate 32% Reduction in RLR Related Crashes Tried

8-28 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

8-29 Traffic Signals Countermeasures– Exercise XI: Poughkeepsie NY  What low cost safety countermeaures would you consider?  What is the safety effect (CRF) for each? Discussion

8-30 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

8-31 Left Turn Lanes + Left Turn Phases Add a Left Turn Phase to Existing Signal Tried *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation CRF = 23% to 48% Total Crashes CRF = 63% to 70% Left Turn Crashes

8-32 Left Turn Lanes + Left Turn Phases Add a Protected/Permissive Left Turn Phase to Existing Signal Tried *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation CRF = 4% to 10% Total Crashes CRF = 40% to 64% Left Turn Crashes

8-33 Left Turn Lanes + Left Turn Phases Add a Left Turn Phase + Left Turn Lane to Existing Signal Tried *NCHRP 500, Objective 17.2 A1 – Employ Left Turn Signal Phase CRF = 35% Total Crashes CRF = 58% (Iowa), Left Turn Crashes

8-34 Left Turn Lanes + Left Turn Phases Signalize and Add a Left Turn Lane without Left Turn Phase Tried *NCHRP 500, Objective 17.2 A1 – Employ Multiphase Signal Operation CRF = 15% Total Crashes CRF = 21% to 25% Total Crashes CRF = 46% to 54% Left Turn Crashes

8-35 Left Turn Lanes + Left Turn Phases Signalize and Add a Left Turn Lane + Left Turn Phase Tried 58% Reduction in Crashes, *Iowa *NCHRP 500, Objective 17.2 A1 – Provide Left Turn Signal Phase CRF=25% to 36% Total Crashes CRF=43% to 45%, Left Turn Crashes

8-36 Change Permissive Left to Protected Left Only CRF = 97% to 98% Left Turning Crashes * Winston-Salem, NC Proven *NCHRP 500, Objective 17.2 A1 – Provide Protected Left Turn Signal Phase

8-37 Add Signal Ahead Advance Warning Sign Tried CRF= 35-40%  Winston- Salem, NC  McGee  MN DOT

8-38 Add Signal Ahead Advance Warning Sign Tried TreatmentFinding 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

8-39 Add Advance Warning Sign with Active Flashers tied to Signal Operation CRF=35% to 67% Reduction in RLR Related Crashes, *Bonneson Tried

8-40 Add Advance Warning Signs & Flashers Tried 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

8-41 Add Supplemental Signal Head(s) Supplemental Far Left Signal Head

8-42 Add Supplemental Signal Head(s)  Crest Vertical Curve + Right Hand Curve  Sight Distance is Limited By Noise Walls

8-43 Overhead Red “T” Signal Heads Tried CRF = 12% total crashes CRF = 33% Reduction in Rt angle crashes, *Winston-Salem, NC

8-44 Flashing Operation IssueBenefitDetriment  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

8-45 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

8-46 Signal Coordination Proven *NCHRP 500, Objective 17.2 A4 – Employ Signal Coordination CRF = 15% to 17% total crashes – 5 studies CRF = 25% to 38% Right Angle Crashes

8-47 Traffic Signals Available thru ITE ITE website: Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red Light Running *NCHRP 500, Objective 17.2 E-3 – Implement Automated Enforcement of Red-Light Running Proven

8-48 Traffic Signals Review Question: What is the Recommended Practice re Calculation of Change Intervals? CP = t + V/2a + V/20*64.4*g + (W+L)/V ITE Traffic Engineering Handbook -reduces RLR frequency by 50-70% CRF = 4 to 31% Total Crashes CRF = 1 to 30% Right Angle Crashes

8-49 Traffic Signals Learning Outcomes: 1.Identify countermeasures for operation and design deficiencies of traffic signals

8-50 Questions? Traffic Signals