A Trifling Place
3:27 pm
Wed March 20, 2013

A Trifling Place, Episode 7: Turn Green Already!

Welcome to “A Trifling Place,” a podcast dedicated to exploring the ins-and-outs of Charlotte.

Find out how Charlotte's traffic signals work

Every city has its share of traffic issues. In Charlotte, for example, there are a lot of complaints about rush hour near Ballantyne on I-485. (Relief is coming. That section of the road is scheduled to be expanded to three lanes by December 2014.)

But today we're not talking about the quality of the Charlotte region’s roads. We’ll focus on an issue the Charlotte Department of Transportation has a little more control over: traffic lights.

I only moved here in August, so I’ve asked veteran WFAE reporter Lisa Miller to help me out …

Credit Tasnim Shamma

TS: So how was your commute this morning?
LM: Well, it was OK. As you know, there have been a few times I’ve complained about the traffic lights in Charlotte.
TS: Yeah I know. Tell me again. What’s wrong with the traffic lights here?
LM: OK. Well I always seem to get stuck at the red lights and then they seem to last so long. And the worst thing is when the light turns green and the car in front of you doesn’t move

So we hit road to investigate.

TS: It is 8:16 a.m. and we are driving towards Charlotte from the University area. 
LM: We're on Tryon right now. So this is actually for a long time my route home. Until I got so fed up with all the traffic lights and the timing that I decided just to take the highways.   

We’re joined by a traffic expert. He’s Martin Kane, a professor at UNC Charlotte’s civil and environmental engineering department . 

The Charlotte Hub And Spoke 

"Charlotte, primarily with exception of the downtown area is built like what are called a Hub and Spoke type system," Kane says. "You have the central core, which is laid out pretty much in a grid pattern." 

And once you leave the Center City, we have streets like Tryon and Providence that branch out like the spokes of a wheel. It’s these streets that are especially problematic, Kane says, because "if you don't have consistent spacing throughout the whole corridor like in this case, it's very hard to make that work in both directions.

"So that's one of the big problems that traffic engineers are trying to deal with. So we try to get it so that everyone is equally unhappy."

But today’s drive is smooth cruising. I’m kind of disappointed. I wanted to see what Lisa occasionally gripes about. Kane offers that he is our good luck charm. We agree. 

But our luck ran out when we came to Providence and Queens. CDOT warned us about this intersection.

Professor Kane says when people are stuck in traffic, they could occupy themselves by flashing their lights -- at least when the sun’s out.

Lisa likes this idea. She asks him what he does. Kane says he almost never sits in traffic because he plans his routes and knows when the roads are busy. If it's busy, he just doesn't go out.

'Not A Joyride'

But as reporters, Lisa and I have to leave whenever news breaks.

TS: So whenever I'm trying to go to the Government Center there's always this long line when I'm trying to make a left turn here, on East 4th Street.
LM: Are we going to make it? Are we going to make it on one green? It looks we're going to do it this time! Sometimes it takes me a couple.

Here, Kane explains, it actually depends on the cars in front of you. The detector is counting the number of cars, but it's also measuring the time between vehicles. So for example, we were third in line at the intersection. If the light turns green and the first car goes, but the driver of the second car is drinking coffee or daydreaming and they stall before turning, the detector counts the first vehicle, but then it senses there's a big gap between the first car and the second car. So what happens then is the cycle cuts short because it thinks there's not a lot of traffic. So that second car will get through, but we won't.

Professor Kane finds this frustrating.

"The objective during this time is commuting," he says. "We're trying to get from point A to point B. This is not a -- shouldn't be -- a joyride. When the light turns green, I like it when people are paying attention to what's going on.  When they cause that cycle to shorten, that irritates me. Because if I'm behind them, there's a good chance I might not get through the intersection. So they didn't suffer for their lack of attention. I did."

Just a few minutes later, we were waiting in another left turn lane on South Boulevard and the Belk Freeway. Lisa stalls and gets honked at. 

The Control Room

After our car ride with Professor Kane, I still had a few more questions about the city's 736 traffic signals.

I met up with Charles Abel, the city's transportation systems manager at one of the city's transportation management centers. It's in the basement of Charlotte's old city hall across the Government Center.

The walls are lined with large TVs that streams video from nine of the 300 traffic cameras in the city. There are half a dozen computers that technicians use to choose which intersections they need to monitor. They look out for accident alerts from the CMPD and pass them on to the media so that we can notify commuters. They bring up those intersections on the screen to see what they can do to help. 

"If they see something like maybe there’s an accident and one leg of the road is closed, and all the traffic’s being diverted at that point, then they could change the timing at that intersection," Abel says. "So that say the left turn, which normally would only get, for example, 16 seconds, we would change it so that it would get 40 seconds or something like that, to help people get through that intersection."

There are only two signal technicians who work out of the CMPD law enforcement center during peak traffic hours in the morning (6:30 to 9:30 a.m.) and evening (3:30 to 6:30 p.m.). Abel uses a joystick to zoom into intersections on the large TV displays. I asked him to zoom into the intersection where Lisa and I had been waiting for a really long time: Providence and Queens. 

On the screen we can see that they had built a new curb at that intersection. And I do remember now that there was a lot of construction where we were waiting. At most intersections, you'll see incision marks in the pavement where the wire runs underground. It detects the metal from your car when you run over it and sends the information up the pole to the traffic signal box.

"We have vehicle detectors that are in the pavement. And when they come through with construction like that, it tears out all our detectors. And once we lose detection, then we're pretty much having to guess what the traffic's going to be."

For the last 50 years, Charlotte has been using wires underneath the pavement to detect traffic. More recently it's been experimenting with video, microwave and heat imaging to figure out which method works best.  But the loop detectors are still the most reliable method of detection.

(A tip from CDOT: The two-inch white line across the road at a signalized intersection is not only there to guide you as to where to stop but is where the detection zone begins. If you move past it, you become invisible to the traffic signal controller and you will not get a green.)

Traffic King of Charlotte

While we were driving back to the office, I had one last question for Professor Kane.

TS: If you had all the money in the world, how would you improve our traffic system?
LM: King of Charlotte.
KANE: Whew. That's a good question. I don’t know. All the money is not going to fix all the traffic problems. A city is necessarily congested because you have tightly packed areas for business and residential. And so there, you're going to get traffic congestion that goes along with that. Maybe another thing to do with all the money in the world is try to come up with some ways to encourage people to use different modes of travel, whether it's walking or bicycling or riding the bus or the light rail or taking their automobile. 

So that's what the temporary traffic king of Charlotte would do. Basically, if you want to live in a city, get used to it.