LOW COST SAFETY IMPROVEMENTS

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


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


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


At 450 feet back

MUTCD Requires 460 feet of visibility

Southbound Naper Blvd approaching Plank Road

Traffic Signals




At 280 feet back from Stop Bar

Traffic Signals


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


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



Additional Supplemental Near-Side Signal

Traffic Signals


Signal Timing /Coordination Visibility Improvement

Additional Supplemental Near-Side Signal At 450 feet

back from Stop Bar

Traffic Signals



Additional Supplemental Near-Side Signal

Southbound Naper Blvd at Ogden Av toward Plank Road

Traffic Signals



Advance Warning Sign with Yellow Flasher


Traffic Signals


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

LOW COST SAFETY IMPROVEMENTS

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