DATE: June 25, 2015
TO: Board of Mayor and Aldermen
FROM: Eric Stuckey, City Administrator
David Parker, City Engineer/CIP Executive
Joe York, Director of Streets
Paul Holzen, Director of Engineering
Carl Baughman, Traffic/Transportation Engineer 3
SUBJECT:
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Discussion of the Application of a Flashing Yellow Left Turn Arrow on Hillsboro Road at Fieldstone Parkway
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Purpose
The purpose of this memo is to provide information to the Franklin Board of Mayor and Aldermen (BOMA) concerning a new type of traffic signal control at the intersection of Hillsboro Road and Fieldstone Parkway, with left turn crash problems. The Flashing Yellow Arrow (FYA) left turn display was approved by the federal Manual on Uniform Traffic Control Devices in 2009. A national study demonstrated that drivers had fewer crashes when using the Flashing Yellow Arrow left-turn signal than with the traditional circular green left-turn signal, because some drivers perceive any green signal to mean GO. The traffic signal at the subject location has experienced severe green ball left turn crashes that can be overcome with the application of the FYA.
Background
The subject intersection operates as a typical four-legged intersection, with dedicated left turn lanes and protected/permitted left turn phasing (PPLT) on all approaches. The primary crash experience is where left turns from Hillsboro Road turn into oncoming traffic while attempting to enter Fieldstone Parkway. A factor contributing to this pattern is high speeds on Hillsboro Road, therefore offering challenges for turning vehicles to judge the length of gaps in oncoming traffic.
The FYA operation has been shown by research and experience to be intuitively understood by motorists as a left turn movement to be made with caution. For clarification, a sign may be added such as "Left Turns Yield on Flashing Yellow Arrow". The first application of FYA in Franklin was successfully installed in April 2015 at the intersection of Mallory Station Road and Duke Drive/General George Patton Drive, where it overcame the limitations of protected-only left turns due to the offset in the side streets at a railroad crossing.
Data
The National Cooperative Highway Research Program (NCHRP) investigated the crash experience when PPLT signals were converted into Flashing Yellow Arrow Protected Permitted Left Turns (FYA PPLT). Figure 23, which is attached, from NCHRP 123 Evaluation of FYA Permissive-Only Left-Turn Indication Field Implementation indicates that as more select locations are converted from PPLT control to FYA PPLT, the average crash rate decreases substantially over time. These findings apply even where only the major street PPLTs were converted, while leaving the minor street PPLTs unconverted.
This result suggests that a program of such conversions could provide safety benefits throughout the City, particularly where high-speed approaches oppose the left turn movement.
To accomplish the PPLT conversion at this intersection, the following new equipment would be needed:
· Signal cabinet to accommodate the FYA PPLT phasing
· Controller with FYA firmware
· Conflict Monitor with FYA monitoring
· 4-section signal heads (2 each). These would be span-wire mounted, but their location over the intersection is generally outside of the tracking path of vehicles, minimizing their potential for knockdown.
If this PPLT conversion is approved, there should be an educational campaign, along with its installation, on the order of the City's first FYA, as well as the instructional signs at the intersection
Options
The available options evaluated by staff are as follows:
1. Implement FYA proposal - offers crash reduction potential based on research experience.
2. Install protected-only phasing - offers practical assured crash reductions at the expense of significant motorist delays which are deemed not necessary with the application of Option 1.
3. No action - considers that the crash experience is acceptable (the crash rate is in the lower range of acceptability, but the severities of these crashes is unacceptable, due to high speeds involved).
Financial Impact
The estimated financial impacts are as follows:
· Option 1- Signs ($200), signal heads ($1,800), conflict monitor ($800), controller ($2,100), cabinet ($5,000). Installation labor to be performed in-house by the Streets Department. Total cost $9,900.
· Option 2 - Signal heads ($1,200). Cost of unnecessary motorist delay on generally every cycle.
· Option 3 - No cost.
Recommendation
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This is a status update and staff plans to proceed with the implementation of Option 1 at an estimated cost of $9,900. The costs for this upgrade will be shared between the Streets and Engineering Departments approved annual budget.
In summary, the application of the Hillsboro Road FYA left turns is the best solution for this special situation and offers potential for safety improvements at other left turn hazard situations.