# Presentation: 321587

## City of Little RockDallas Phasing ImplementationRodney Parham Road

- William Henry, P.E.
- Traffic Engineering Manager

## 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

## 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.

## 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

## Time Space Relationship

- Lead-Lag Operation corrects inefficiencies due to unfavorable spacing of traffic signals along the corridor

**Efficiency is improved when providing early releases to keep the main traffic platoon moving**

## Project Location

- Rodney Parham Road – 2.6 mile Arterial

## Project Scope

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

## 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

## Synchro Solution

## 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.

## 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

## Adjusted 2-Way Plan

## 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

## Left Turn Split Reduction Examples

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

## Dallas Display

- Signal Head Louvered for the Leading Left Phase Direction

## Dallas Displays

- Doghouse 5-Section Signal w/louvers

## Dallas Display for Leading Movement

- Display Prevents Yellow Trap

## Breckenridge Overlaps for Dallas Displays

## Epac Overlap Programming for Breckenridge

## Eastbound on Rodney Parham – Noon Plan

## Westbound Rodney Parham – Noon Plan

## Completion of Timing Plan

- Plans are never complete, constant adjusting due to changing patterns
- Next Improvement scheduled     ** Traffic Responsive **

## Contact Info

- Bill Henry
- 501-379-1816
- _[BHenry@littlerock.org](mailto:BHenry@littlerock.org)_