Field Implementation Study
Flashing Yellow Arrow
NCHRP 3-54 (2)
Evaluation of Traffic Signal Displays for
Protected Permitted Left Turn Control
August 30, 2000
1
Field Implementation Study
Flashing Yellow Arrow Testing
NCHRP 3-54 (2)
Evaluation of Traffic Signal Displays for
Protected Permitted Left Turn Control
Kittelson & Associates, Inc.
2200 W. Commercial Boulevard, Suite 304
Ft. Lauderdale, Florida 33309
610 SW Alder Street, Suite 700
Portland, Oregon 97205
University of Massachusetts – Amherst
Transportation Center
214 Marston Hall
Amherst, Massachusetts 01003-5202
August 30May 15, 2000, 2000
1
NCHRP 3-54 (2) Implementation Plan
Purpose of this Document
In January 1995, the National Cooperative Highway Research Program (NCHRP) initiated a new research project intended to address potential confusion caused by the variety of protected/permissive signal displays currently in use. Under the guidance of the NCHRP program, that study has now progressed through research plan formulation and implementation stages. As part of the continuing research activities associated with the project, the project team is preparing to initiate field implementation studies at select locations across the country to test the flashing yellow arrow permitted indication performance.
This implementation study will identify volunteer agencies that will convert existing signalized intersections operating with protected-permitted left-turn control that current use the standard MUTCD green ball display for the permissive interval to using the flashing yellow arrow display for the permissive interval.
The purpose of this document is to inform operating agencies about the NCHRP study on protected/permissive displays and to solicit their participation in the studies. Included in this document is a brief background summary of the project’s objectives, a description of the project activities completed to date, information explaining the purpose of the implementation study, and documentation of the data requirements of the implementation study.
Project Background
The Need for the Project
There are several advantages associated with protected/permissive left-turn (PPLT) phasing such as reduced delay, improved progression, reduced fuel consumption, and reduced air pollution. There area also several disadvantages including potential motorist confusion and, if not implemented safely, the “yellow trap.” Fortunately, many practicing agencies have found the advantages to outweigh the disadvantages.
Several innovative signal displays and phase sequence patterns have been developed to diminish the disadvantages of PPLT phasing and are currently in use at various locations throughout the country. These innovative PPLT signal displays use three- and four-section head arrangements and include at least four variations of the permissive indication including the flashing circular red, the flashing circular yellow, the flashing red arrow, and the flashing yellow arrow. Other variations also exist in phasing, signal display, arrangement, signal placement, and use of supplemental signs. Examples of these displays and the locations that currently use them are shown in Figure 1.
The current PPLT standard allowed under the MUTCD provides uniformity in the left-turn treatment; however, the MUTCD is an evolving standard and many displays used throughout the United States (including those shown in Figure 1) are not considered to be in conformity. Those non-conforming displays are used because they continue to be promoted by some practicing traffic professionals. The National Committee on Uniform Traffic Control Devices (NCUTCD) has expressed concern that the variety of PPLT controls currently used may confuse motorists traveling throughout the United States. In response to this concern, the National Committee has been the leading force behind this comprehensive national study to validate the operational advantages and safety aspects of the various PPLT signal displays including signal arrangements and permitted indications.
Project Objective
The objective of the NCHRP 3-54 project is to evaluate the safety and effectiveness of different signal displays and phasing for protected/permissive left-turn control (PPLT). Several laboratory and field studies have been and will be completed to meet this objective. These studies will gather, analyze, and interpret data that will serve as the basis for recommendations toward a uniform display used for PPLT signal control. The research considers both leading and lagging operations associated with PPLT control, situations where the yellow trap occurs, and typical display arrangements.
It is important to note that the NCHRP 3-54 project will not develop any guidelines, warrants, or recommendations for the use of PPLT phasing. The underlying assumption is that the traffic engineer has decided that PPLT control is the most appropriate left-turn treatment. The goal of the NCHRP 3-54 project is to identify the most effective display(s) to be used with PPLT phasing, maximizing driver understanding and safety.
Project Status
The Contractor (Kittelson & Associates, Inc. in association with the Texas Transportation Institute and U-Mass?) has completed several studies on all of the known PPLT signal display variations currently in use across the United States. Both scientific and empirical methods have been used in continuing efforts to advance the research project. The study work activities completed to date include:
· Conducted a comprehensive national agency survey to identify the magnitude and types of PPLT signal phasing and displays throughout the United States.
· Developed and administered a semi-dynamic driver survey to evaluate driver’s understanding of PPLT signal displays and indications currently in use.
· Conducted field studies in eight cities across the country evaluating operational and capacity issues including: start-up lost time, saturation flow rate, and follow-up headway.
· Evaluated safety issues through conflict studies and a comparative review of crash data.
Additionally, the Contractor evaluated all of the displays using engineering assessment techniques. This engineering assessment considered safety, operations, implementability, human factors and versatility in assessing the feasibility of each PPLT display type.
These studies have been documented in a series of working papers that describe key study work activities, study methodology, results, findings and, in some cases, conclusions.
In addition to the working papers, the Contractor produced the first interim project report in September 1999[1]. In October 1999, the Contractor met with their project panel members and discussed the project’s findings. The project panel approved all of the work activities conducted by the Contractor to date and also approved an amended study approach to further study a select few permissive displays. Three PPLT displays were identified for further study; the current MUTCD green ball, the green ball as used in the Dallas Display, and the flashing yellow arrow display.
Under the amended study approach, the Contractor (Kittelson & Associates, the Texas Transportation Institute and University of Massachusetts) will be employing the use of a driver simulator to evaluate the three permissive displays identified for further study. While the flashing yellow arrow has been well understood by drivers in the research work completed to date and is expected to perform well in the driver simulation studies, this display has the least actual field use of the three PPLT displays being further studied.
To address the lack of field applications of the flashing yellow arrow PPLT display, the project panel also approved the study of this display in the field as part of the amended study. The purpose of the field implementation study is to document how the flashing yellow arrow display can be implemented, including documentation of any technical or political issues as well as safety and cost implications associated with implementing this display. The project panel felt strongly that this task was needed before such a display, if deemed “best” understood, could be recommended to the National Committee on Uniform Traffic Control Devices. The project panel is not recommending the implementation of the flashing yellow arrow at this time. Instead, they are seeking further evidence and support that this display is a safer and better understoodbetter-understood display than what is currently allowed in the MUTCD.
Field Implementation Study
Background
The field implementation study was initiated aThe field implementation study was initiated at the request of the project panel to collect so that actual field data on the flashing yellow arrow displaycould be sourced. The implementation study will collect crash data and conflict data to record the safety performance associated with the flashing yellow arrow display. The implementation study will also collect field operational data, such as start- up lost time and saturation flow rate data, to quantify the operational impacts. The implementation study will monitor field installation by the operating agency and document techniques and issues resolved (e.g., control logic) for successful implementation to be achieved.
Schedule
Implementation of the flashing yellow arrow display began in May 2000. Several local agencies are now committed and moving forward with FHWA approval for use of an experimental device. The NCHRP 3 54 Contractor will be completing analysis of data collected for the experimental implementation in late Fall 2000. The documentation of before/after data (all data) and local agency reaction is planned for late November 2000.It is our hope that field implementation will occur during the summer 2000. To facilitate the data collection process, the University of Massachusetts has prepared a detailed data collection plan for the project. A copy of this plan, which provides documentation of the steps necessary for field data collection, is attached.
A tentative scheduled for the field implementation plan is outlined below:
May 1st Collection of before data
May 15th Change over to flashing yellow arrow display
June 16 – August 15 Evaluation
August 16 – 24 Collection of after data
September 15 Documentation
Identification of Volunteer Agencies
The Contractor research team wwill identify eight locations/agencies for field implementation. These locations will be identified based upon geographic location, type of PPLT design currently in place, and the desire of the agency to participate. The objective of the implementation study will be to evaluate the flashing yellow arrow display.
Each of the eight Vvolunteering agencies will be responsibilitiesle for:
· Identifying a minimum of three intersections for installing the flashing yellow arrow display on at least one intersection approach.
· Install or retrofit the appropriate signal arrangements (head). See below for more instruction on the signal head arrangements.
· Make the necessary modifications, if any, to the existing signal controller and controller conflict monitor.
· Collect 16 hours of before and after video tape at a minimum of three intersection approaches that will have the flashing yellow arrow display.
· Collect 16 hours of before and after video tape at a minimum of three intersections that are considered as control intersections. See below forof specifications.
· Provide intersection data sheets for each location. See below.
· Provide three years of before crash data and one year after crash data. It is requested that volunteer agency supply a total of three years of after data and this data would be forwarded directly to NCHRP for further study at a later date.
· Track and report change over costs and implementation issues.
· Submit overall qualitative statement on the flashing yellow arrow operation.
The Contractor will be responsibilitiese for:
· Assist the agency in identifying good candidate installation locations.
· Provide assistance to the agency to issue resolving related to installing the flashing yellow arrow display.
· Provide a form letter to submit to from the Federal Highway Administration (FHWA) requesting authorization ing thefor the volunteer agency to implement for instathe flashing yellow arrow display llation of as an experimental display.
· Review and analyze the before before and after video tape data.
· Summarize and analyze the crash data.
· Collect andA analyze field operational data.
· Collect and Aanalyze field conflict data.
Expected Characteristics of Study Intersections
The PPLT intersections selected should be considered a typical intersection containing no unique geometric or operational features. The PPLT intersection should be a right angle intersection with four approaches of two or three through lanes each, contain exclusive left-turn lanes(s) on the study approach, display (currently) the green arrow indication for the protected left-turn movement and the green ball indication for the permitted left-turn indication, have a relatively flat grade, 12-foot lane width, no on-street parking[2], and no additional variables that directly impact the left-turn movement being evaluated. Intersections should be different only in PPLT display arrangement and permitted indication.
At least three (3) of the intersections selected should be those proposed for improvement (i.e., installation of the new PPLT signal display). Three (3) additional intersections should be selected that will not receive any improvements during the study period. These intersections will act as control sites. Therefore, a minimum of six study sites are required.
Proposed Flashing Yellow Arrow Display Arrangements
The research team, in partnership with project panel members and the projectand technical advisory group members, has identified several display arrangements that demonstrate good motorist understanding. Different display arrangements are recommended for an exclusive left-turn display and shared display.
Exclusive Display Arrangements
The flashing yellow arrow (FYA) display is intended as an exclusive turn display. The proposed display consists of four arrows - red, steady yellow, flashing yellow, and green. This display has many advantages, one of which is flexibility in application. The all-arrows display can be used for left or right turns. The remainder of discussion has been limited to left turn applications, more specifically, protected/permitted left turns.
There are at least four possible PPLT signal displays that are recommended for installation of the flashing yellow arrow display at a location where there is an exclusive left-turn lane and the left-turn display is a separate display (not used by the adjacent through movements). Those alternative displays are shown in Figure 2 below. As shown in Figure 2, the display can be implemented in four different head configurations, using three or four sections and horizontal or vertical alignments. The three-section head options involve shared use of a bi-modal section by the green and flashing yellow arrows. The three-section arrangement may be desired for clearance purposes or for ease of implementation if an existing three-section arrangement is available. The signal arrangement can be mounted either vertically or horizontally.