The National Academies

NCHRP 03-125 [Final]

Evaluation of Change and Clearance Intervals Prior to the Flashing Yellow Arrow Permissive Left-Turn Indication

  Project Data
Funds: $300,000
Research Agency: University of Wisconsin-Madison
Principal Investigator: David Noyce
Effective Date: 9/21/2016
Completion Date: 12/30/2022
Comments: Published as NCHRP WOD 394.

The flashing yellow arrow (FYA) has been the focus of many research efforts over the past 20 years. Those efforts culminated in the inclusion of the FYA as a permissive left-turn and right-turn indication in the 2009 Manual on Uniform Traffic Control Devices (MUTCD). Implementation of FYA across the country has rapidly increased with hundreds of installations by cities and states. An alternative to the FYA is the flashing red arrow (FRA) that is available when stopping before turning is desired. Some agencies have adopted the FRA as their standard permissive left-turn indication.
One of the issues with the implementation of the FYA/FRA indications that has not been effectively addressed is the change and clearance interval sequence prior to the permissive interval that most effectively communicates the desired action to road users. For example, many jurisdictions use both the yellow arrow change indication and the red arrow clearance indication when transitioning from the protected movement to the FYA. Although not currently required by the MUTCD, some traffic engineers believe that the solid red arrow is needed to effectively communicate to drivers that the left-turn movement has switched from protected to permissive. Other traffic engineers allow an immediate transition from the solid yellow arrow change interval to the permissive indication. The human factors and operational impacts of these alternative sequences have not been explored and traffic engineers need guidance.
Tradeoffs between safety and operational efficiency are common in all aspects of transportation engineering. Determining an appropriate balance is often difficult due to the number of confounding factors. In this case, a direct assessment of the safety performance of the alternative indication sequences is cost prohibitive due to the difficulty in determining whether the change and clearance intervals contributed to a crash and the likely small number of these types of crashes. A human factors approach is therefore being taken. This research is intended to provide greater clarity on the performance of these alternative sequences so that, to the extent feasible, a tradeoff assessment can be made using data rather than perceptions.
Some agencies are using a solid red arrow between the protected and permitted intervals for purposes other than clearance. Examples include providing time for an opposing queue to process or as a leading pedestrian interval. These types of applications are not being addressed in this research.
The objective of this research was to develop guidelines for the use of solid yellow arrow change and solid red arrow clearance intervals after a leading solid green arrow transitioning to a permissive FYA or FRA based upon their human factors and efficiency implications. 
STATUS: The final report was published as NCHRP Web-Only Document 394: Evaluation of Change and Clearance Intervals Prior to the Flashing Yellow Arrow Permissive Left-Turn Indication.

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