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LOW COST SAFETY IMPROVEMENTS
Practitioner Workshop
The Tools –
Traffic Signals – Session #7
Traffic Signals
Learning Objectives:
Recognize Deficiencies in Operation/Design of Traffic Signals
Select appropriate Enhanced Application Countermeasures for Traffic Signals
Traffic Signals
Safety Benefits of Signalization: Traffic Control (3 and 4 approach
Stop Controlled - >>>>>> Signal Control)
* NCHRP 491 “Index of Effectiveness” = AMF
0.86 0.77
All All
Traffic Signals
Traffic Signal 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
Traffic SignalsTraffic Signal 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
Traffic SignalsCountermeasures:
1. Update Yellow Clearance Interval
All-Red TimeYellow Time
ITE Traffic Engineering Handbook
Traffic SignalsCountermeasures:
1. Update Yellow Clearance Interval
Red TimeYellow 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
= 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
Yellow Time
Traffic SignalsCountermeasures:
1. Update
Yellow
Clearance
Interval
*TTI, Bonneson, 2003
Traffic Signals
Countermeasures:2. Modifying Clearance Intervals
* From High Volume Signalized Intersection Handbook
Traffic Signals
Intersection Countermeasures:2. Add All-Red Clearance Interval
ITE Traffic Engineering Handbook – All-Red Clearance Interval
T = ( W + L) / V
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
CRF=25% for Add 1.0 Sec
*Bhesania, 1991
Traffic Signals
Countermeasures:3. Improve Visibility (12” Indications, Suppl
heads)
Mast Arm Signals* Iowa
8” to 12” Indications, *Winston-Salem, NC
CRF = 32% Related Crashes
CRF = 48% Related Crashes
Traffic Signals
Countermeasures:3. Improve Visibility (Mast Arms) Signal Head
per lane
48% in Right Angle Crashes, *Winston-Salem, NC
Supplemental Near SideSupplemental
Far Side
22% in Total Crashes
9% in Fatal & Injury Crashes, British Columbia
Traffic Signals
Countermeasures:4. Add Back Plates
25% to 53% reduction of RLR related Crashes Bonneson, Winston-Salem, NC
No Back Plates Back Plates
Traffic Signals
Countermeasures:4. Add Back Plates
Canadian retro- reflectorized backplate
32% reduction in RLR Crashes
Traffic Signals
Countermeasures:5. Change Permissive Left to Protected Only
-97% Reduction in Left Turning Crashes
* Winston-Salem, NC
Traffic Signals
Countermeasures:5. Add a Turn Phase to Existing Signal
36% Reduction in Crashes, * Iowa
58% Reduction in Crashes when add Turn Phase and Turn Lane, *Iowa
Traffic Signals
Countermeasures:6. Add Advance Warning Sign with Active
Flashers
35% to 67% Reduction in RLR Related Crashes, *Bonneson
Add Signal Ahead Signs, * Winston-Salem, NC
Traffic Signals
Countermeasures:7. Add Supplemental Signal Head(s)
Supplemental Far Left Signal Head
Traffic Signals
Countermeasures:8. Use of Overhead RED “T” Signal Heads
35% Reduction in RLR Crashes, *Winston-Salem, NC
Traffic Signals
Countermeasures:9. Flashing Operation
Change late night flash of Yellow on mainline/Red on side street to normal operating traffic signal mode
Traffic Signals
Countermeasures:10. Signal Coordination
12% Reduction in Peak Hour Crashes - Naperville, IL
25% Reduction in Crashes – San Buenaventura, CA
Traffic Signals
Countermeasures:11. Signal Controllers and Actuation
Traffic Signals
Case Study: Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination and Visibility Improvement
Southbound Naper Blvd at Ogden Av toward Plank Road
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination and Visibility Improvement
At 450 feet back
MUTCD Requires 460 feet of visibility
Southbound Naper Blvd approaching Plank Road
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination and Visibility Improvement
Southbound Naper Blvd approaching Plank Road
At 280 feet back from Stop Bar
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Investigation identified that the county highway agency had made changes in the interconnect system and that the operation of the traffic signal at Plank was no longer coordinated with the signal at a major intersection to the north; coordinated operation was restored.
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Review of the engineering plans identified that the signal design was for tangent approaches; the actual conditions in the field were a reverse 35 mph 6 degree curve.
Signal heads were far side only with 12” sections and
backplates
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination and Visibility Improvement
Additional Supplemental Near-Side Signal
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination and Visibility Improvement
Additional Supplemental Near-Side Signal
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination Visibility Improvement
Additional Supplemental Near-Side Signal At 450 feet
back from Stop Bar
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination Visibility Improvement
Additional Supplemental Near-Side Signal
Southbound Naper Blvd at Ogden Av toward Plank Road
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination Visibility Improvement
Advance Warning Sign with Yellow Flasher
Southbound Naper Blvd approaching Plank Road
Traffic Signals
Case Study : Remedy of Naper Blvd & Plank Road Traffic Signal
Signal Timing /Coordination Visibility ImprovementAdvance Warning Sign “Be Prepared to Stop” with “When Flashing” Plaque with Flasher tied to Controller
Northbound Naper Blvd approaching Plank Road
Questions?
Traffic Signals