T3 Webinar:

Arterial Traffic Signal Timing: Addressing Technical and Inter-Jurisdictional Challenges)

September 11, 2007

Text version of Webinar presentation:

"City of Little Rock, Dallas, Phasing Implementation, Rodney Parham Road"

Description of image or images on a slide contained in brackets.

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Slide 1: City of Little Rock

Dallas Phasing Implementation
Rodney Parham Road
William Henry, P.E.
Traffic Engineering Manager

Slide 2: Protected Permitted Left Turns (PPLT)

Provides drivers with the option to wait for a protected left turn when there are insufficient gaps or to make a left when there are available gaps to make the turn.
PPLT increases efficiency over fully protected left turn phasing
Approximately 30% of intersections in the US include PPLT phasing

Slide 3: PPLT Phasing Concerns

PPLT phasing can cause a "Yellow Trap".
A yellow trap occurs when a driver waiting to make a permitted left turn sees the adjacent through phase turn yellow while the opposing green phase stays green.

Slide 4: Correcting the Yellow Trap with the Dallas Display

Dallas Phasing utilizes an exclusive left turn signal head with the green and yellow ball displays louvered to prevent adjacent lanes from seeing the signal indications
The louvered display shows the opposing through indication instead of the adjacent through indication to eliminate the yellow trap

Slide 5: Time Space Relationship

[Image of TS/PP (Time-Space/Platoon-Progression) diagram that shows how lead-lag operation corrects inefficiencies due to unfavorable spacing of traffic signals along corridors.]

Slide 6: Project Location

[Topographical map showing project location on Rodney Parham Road.]

Slide 7: Project Scope

Coordinate 11 Signals
Utilize Synchro for Initial Timings
Implement Lead-Lag Left Turn Phasing.using Dallas Display
Develop System Cycle Length
Optimize Cycle and Splits – Synchro
Export Data to TSPPD
Evaluate Time Space Diagram Solution Provided by Synchro

Slide 8: Noon Peak Flows — 2006

Shackleford 1427 WB 1258 EB
Breckenridge 1181 WB 1074 EB
Reservoir Rd 973 WB 915 EB
Brookside 449 WB 1443 EB

Slide 9: Synchro Solution

[Image of TS/PP diagram that displays a synchronized solution.]

Slide 10: Synchro Signal Progression

40 MPH Design Speed
Balanced Noon Flows
1000–1400 vehicle per hour flows
Synchro Model only reduces intersection delays, does not look at arterial flows and the benefits of 2–way progression.
Left Turn splits are excessive, and do not utilize the natural gaps in traffic produced by well designed traffic plans with ample 2–way green bands.
Synchro optimized plan does not provide any significant through traffic bands.

Slide 11: Designing Timing Plans Two–Way Progressive Flows

Utilize Synchro TSPPD Base Plan as a Starting Point
Drive Corridor to establish speeds
Add dummy intersections at both end of the time-space-diagram to aid in developing true two-way progression
With a 100 second cycle, plan for 35 second band widths in each direction for initial design.
Analyze for lead–lag phasing to maximize band widths.
Implement and Adjust Plan

Slide 12: Adjusted 2–Way Plan

[Image of TS/PP diagram that displays an adjusted 2-way plan.]

Slide 13: Two–Way Progression Plan

EB Green Band – 30 Second Band Width – 1427 VPH
WB Green Band – 25 Second Band Width – 1258 VPH
Install Texas Display at 3 intersections in order to run permissive lead–lag left turn phasing
Natural Gaps generated throughout system
Synchro recommended left turn times significantly reduced, which provides more green band time for the major movements

Slide 14: Left Turn Split Reduction Examples

Ark. Valley – Synchro 20 secs. TSPPD Adjusted 10 secs
I-430 West Side – Synchro 44 secs. TSPPD Adjusted 15 secs
I-430 East Side – Synchro 46 secs. TSPPD Adjusted 18 secs

Slide 15: Dallas Display

[Photo of Dallas Display – louvered signal head for the Leading Left Phase Direction.]

Slide 16: Dallas Displays

[Photo of Dallas Display – Doghouse 5–section signal with louvers.]

Slide 17: Dallas Display for Leading Movement

[Photo of Dallas Display for Leading Movement, which prevents yellow trap.]

Slide 18: Breckenridge Overlaps for Dallas Displays

[Aerial photo of Breckenridge overlaps for Dallas Displays.]

Slide 19: Epac Overlap Programming for Breckenridge

[Screenshot of Epac overlap programming for Breckenridge.]

Slide 20: Eastbound on Rodney Parham – Noon Plan

[of Noon Plan for eastbound traffic on Rodney Parham.]

Slide 21: Westbound Rodney Parham – Noon Plan

[of Noon Plan for westbound traffic on Rodney Parham.]

Slide 22: Completion of Timing Plan

Plans are never complete, constant adjusting due to changing patterns
Next Improvement scheduled...

** Traffic Responsive **

Slide 23: Contact Info

Bill Henry
501-379-1816
BHenry@littlerock.org

http://www.pcb.its.dot.gov/res_t3_archive.asp