Communities and transportation professionals strive to provide sufficient peak period travel capacity without creating oversized streets and intersections that operate inefficiently or create off-peak delays.
High numbers of left turns have the potential to upset this balance. While adding a second left turn lane may provide additional peak capacity, it can increase intersection delays for the majority of the day.
A Dual Left Flashing Yellow Arrow (“Dual Left FYA”) has the potential to avoid the downsides associated with typical dual left turn lane operation while still providing sufficient peak period capacity
Dual Left Flashing Yellow Arrow (“Dual Left FYA”)
If there is sufficient “intersection sight distance” for left-turning vehicles to scan the opposing traffic and execute a safe turn, Dual Left Flashing Yellow Arrow may be a viable option.
Typical challenges associated with a second left turn lane
- While a single left turn lane often allows “left turn after yield,” typical North Carolina practice with two left turn lanes has been to restrict left turns to when the solid arrow is shown; i.e., “protected only” lefts
- Restricting left turns to a solid arrow increases delays for left turns – and for everyone else –especially during off-peak because the solid arrow must be displayed even for one vehicle
Benefits of Dual (or single) Left Flashing Yellow Arrow
- Improved coordination– the solid arrow can be displayed anytime in the signal cycle
- Reduced delay – the flashing arrow allows “left turn after yield” (i.e., “permitted”) operation
- Flexible operation – the flashing arrow can be omitted during heavy periods if desired, and/or the solid arrow can be omitted during lighter traffic volumes or all day
A recent case study1 found that Dual Left FYA would lower delay by almost 50%, reduce queue lengths by 20-30%, and save 10,000+ hours of delay per year at an existing Cary intersection.
Examples of Dual Left Flashing Yellow Arrow
- Four North Carolina intersections use Dual Left FYA, with several more planned
- Dual FYA has been used for many years in other cities in the United States, including Richardson and McKinney, Texas; Boulder, Colorado; and Chandler, Arizona.