Answer Man: We live between the two hospitals in Springfield and travel National Avenue nearly every day. The traffic lights on National are timed so you can go from Sunset north at near the speed limit and lights will turn green in front of you. Who determines how the lights change? Are there other timed corridors in our city? — R. Todd Morriss, of Springfield
What a wonderful feeling to have nothing but green lights.
The word used by traffic engineers is "coordinated," not "timed," says Jason Saliba, who does the traffic-light coordination for the city of Springfield. He works in the public works department in traffic management.
The coordination is done hand-in-hand with the Missouri Department of Transportation.
The traffic lights along National are coordinated from 6 a.m. to midnight from the James River Expressway to the Chestnut Expressway, Saliba says. The coordination is done to keep traffic moving by reducing stops.
But catching all greens depends on when you're driving and which way you're going.
For example, most National traffic during morning rush hour is moving south to north. So the lights are coordinated to keep traffic moving northbound. That is reversed during the evening rush hour.
(Keep in mind that just because a vehicle going northbound on National at 7 a.m. has a green light does not necessarily mean a vehicle going southbound on National at the same time and place also has a green light.)
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Saliba wrote via email: "But a driver going the speed limit is not guaranteed a green light. Depending on the time of day and number of vehicles traveling in each direction, there is a preferred direction of travel along each corridor.
"In best case scenarios, it just happens to work out well for both directions."
One variable in coordinating traffic lights, he says, is the amount of traffic on cross streets.
For example, where National intersects with Sunshine Street there is more east/west traffic than where it intersects with, say, Cherokee Street. Therefore, more time is needed for east/west traffic at Sunshine.
"National Avenue happens to be a corridor in which good flow is attainable throughout most of the day," Saliba wrote.
The city has several other coordinated roadways.
"MoDOT maintains about half of the traffic signals in Springfield. State-maintained routes include Glenstone, Kansas Expressway, Chestnut Expressway, Kearney Street, West Bypass, Campbell south of Republic, Sunshine east of Glenstone, and Sunshine west of Kansas Expressway.
"Traffic signals located on all other corridors in Springfield are maintained by the City of Springfield’s Transportation Management Division. City of Springfield and MoDOT traffic signal engineers work very closely to maintain consistent signal timing within Springfield, and even maintaining coordination across jurisdictions.
"So closely actually, that the City signal engineer and MoDOT signal engineers work in the same building."
Keep those questions coming. Send them to The Answer Man at 417-836-1253, spokin@gannett.com, on Twitter @stevepokinNL or by mail to 651 Boonville Ave., Springfield, MO 65806.
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Answer Man: Reader sees nothing but green lights driving National Avenue; why is that? - News-Leader
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