The first prong in the City of Mt. Juliet's adaptive signal project is up and running across the city.
Flashing yellow arrows now blink at proper times at eight signals from Graves Crossing to Pleasant Grove Road.
The total cost for the signal project is about $800,000, said Deputy Public Works Director Andy Barlow.
He said the implementation of flashing yellow arrows is a relatively new concept to the mid-state, but common across the U.S.
"They are proven to increase safety to motorists," he said.
Their basic purpose is to provide an extra alert to the driver that the oncoming traffic has a green light, but vehicles may take a left if there an appropriate gap in the opposing traffic.
"This is different from the way we make a left turn a at traditional signal," he explained. "Typically, we will take a left if the adjacent through lanes have the green ball. If it turns to yellow for the adjacent through movements, then we logically assume the opposing traffic also has the yellow and will be slowing to a stop"
While this has been the case traditionally in Mt. Juliet, it may not be the case with the new adaptive signal system.
In the new system, the adjacent traffic may stop, but the oncoming traffic may not stop. In this scenario, a left turning vehicle's driver may make the erroneous assumption the opposing traffic is slowing to a stop when in fact they have a green ball. This can lead to very serious crashes and is known as the "yellow trap."
With the flashing yellow arrow in place, it communicates to the driver the oncoming traffic still has the green and not to turn in front of oncoming traffic, said Barlow.
Barlow said studies across the U.S. have shown a significant reduction in crashes with the flashing yellow arrow.
One question asked often of Barlow is, can they implement the flashing yellow arrows where there are two left turn lanes. He said this is a significant safety hazard and greatly discouraged to allow traffic from two left turn lanes to turn against oncoming traffic due to sight distance concerns.
Barlow said he will not know the true value of the project until he knows how well the system operates.
But, he said, maximizing the city's signal system is the easiest and cheapest option for improving traffic.
By comparison the cost of widening the road through the corridor to achieve the same result, as a well- coordinated signal system, would cost several million dollars.
The fieldwork is almost complete on the entire adaptive signal project, and the city is working through minor tasks to make sure all the equipment is operating and communicating properly. When complete, signals will be programmed to keep traffic flow at an optimal level.
Writer Laurie Everett can be reached at firstname.lastname@example.org.