Low-cost intersection innovations, part one — a peak and off-peak win for travelers

The regional business community has consistently supported both major freeway improvements as well as low-cost enhancements to intersections and interchanges.

One example is the concept of “Dual Left Flashing Yellow Arrows (FYA).” This involves a signalized intersection with dual left turn lanes that displays – at least for some cycles — a flashing yellow arrow in addition to the green arrow.

Most signalized intersections with dual lefts never display the flashing yellow for those movements, but depending on a variety of factors including volumes and sight distance, it can be possible, and doing so means that some left turners don’t have to wait for a dedicated green arrow to turn, which can save them a minute or more at some locations. It also means that other travelers won’t have to wait for those left turners to travel under a dedicated signal phase, which saves everyone time.

RTA, through the I-40 Regional Partnership, championed consideration of this tool in our region and state, with its initial installation by NCDOT in concert with the Town of Cary at I-40 and Harrison Avenue westbound on-ramp several years ago.

Other dual left FYAs have been installed, including another in Cary a few years ago at Weston Parkway at Evans Road, as well as one in Johnston County.

The newest Dual Left FYA location in our region, and the third in Cary, was activated earlier today — at the intersection of Harrison Avenue and Cary Parkway / Cary Academy entrance.

Cary professional staff confirmed that the signals at all dual left FYA locations operate under a “protected-permitted” display sequence (i.e., dual green arrows followed by a dual flashing yellow arrows) for off-peak periods.

In addition, some of the signals operate with dual flashing yellow arrows during one or both peak periods as well as during off-peak times — meaning that travelers get delay reduction benefits all day.

A prior analysis by RTA Leadership Team member firm Kimley-Horn found that operating the signal at Evans and Weston with dual left flashing yellow arrows would save around 10,000 vehicle-hours of delay per year. Since there aren’t even 10,000 hours in an entire calendar year, that is significant savings for travelers.

Retrofitting an existing dual left turn intersection will typically cost less than $10,000 — so Dual Left FYA can be a very low-cost improvement.

Kudos to NCDOT, the Town of Cary, and other partners for continuing to look for ways to make our roadways more efficient as well as safe.

Joe Milazzo II, PE
RTA Executive Director

RTA is the voice of the regional business community on transportation

post reference: th3.2019.33

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