How North Carolina monitors traffic on 80,000 miles of roads

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Imperfect data from a wide range of sources provides a good overview.

North Carolina's Department of Transportation is responsible for monitoring over 80,000 miles of roads in the state. That's more mileage monitored than any other state in the country except Texas, says State Traffic Operations Engineer Jennifer Portanova. The department needs to know when an accident or other incident is causing a backup anywhere on the road system. But up until recently, she said, they were at the mercy of other departments to let them know.

Today, that's changed: The DoT is using data to transform from a reactive department to a proactive one. 

In three traffic centers, employees are monitoring real-time traffic conditions 24/7 on color-coded digital maps. The data comes from Inrix, a company that  builds a picture of the traffic data from a variety of sources including sensors, crowdsourced traffic information, location, heading, and speed data from commercial fleets and private vehicles. 

The state uses this information not only to figure out what's going wrong at any given moment, but also to plan investments and figure out the likely impact of major projects. It's a perfect example of using a wide range of imperfect data from different sources to make real-world decisions. 

Other solutions too expensive

When the department first began exploring the idea of real-time traffic monitoring, the obvious idea would have been to blanket the state in sensors and have those sensors feed back data to the traffic centers in real time -- a classic Internet of Things scenario. But Portanova says the cost of putting sensors on 80,000 miles of roads was simply prohibitive. While the state has sensors in some high-traffic areas around cities, it couldn't afford to blanket the state with them.

Traffic cameras had the same cost issues, plus it wouldn't make sense to allocate resources to monitor isolated rural back roads in such a comprehensive fashion.

Portanova says North Carolina became aware of Inrix when the company participated in a Request for Proposal (RFP) process as part of a coalition of states looking at a traffic monitoring solution for Interstate 95. The project started with just that single interstate, but expanded to the entire state when the DoT realized Inrix could solve the entire traffic monitoring problem.

In the traffic centers, color-coded maps give traffic monitors an idea what's going on. When the map is green, everything is hunky dory. When it's yellow, traffic has slowed, and when it's red, there's a problem. The monitors will know there's an issue, but the map can't say if it's a five-car pile-up or a red light on a secondary road. It's up to the humans to figure out what the data is telling them and for that they rely on their own experience. For instance, they might know that there's often a backup at a particular spot because of a metering light, or they might see a backup on a four-lane highway where traffic normally wouldn't be stopped and they need to explore further.

When they suspect an incident, the monitors begin to check other sources outside the board. If there's a camera in the area, they can turn on the camera and look for a cause. If not, they have to check with law enforcement and other state and local authorities to figure out what's up.

It's not always perfect, but Inrix gives them enough of an edge that the DoT can be the team letting others know there's an incident. Getting the word out to the public about traffic issues is a big part of the department's mission, and it wasn't nearly as easy before.

Plus, because the department is collecting all this real-time data, it's able to understand historical traffic patterns better, calibrate future traffic demand models, and conduct "What If" scenarios based on this data collection. 

For instance, Portanova says the state is currently planning a major construction project which will involve taking a five-lane road down to two -- what Portanova called "traffic armageddon."  You could assume this will cause some major problems, but rather than using conjecture, the state has projected exactly what the impact will be. This not only helps planning for the project, but also lets the department give affected communities and law enforcement a realistic idea of what to expect.

There has been one stumbling block: Inrix collects information in a different data format than what the DoT was using. Vehicle problems come in on the Inrix map, which has its own orientation format, while the DoT has an existing database of crash information in a different orientation, plus an incidents database in a third format. She said getting all of that information into a single format has proven a challenge, and they are still working on it.

Overall, though, Portanova says the Inrix system system gives them a much better idea what's possible with big data.

"We didn't know what we didn't have. We knew we needed to do more, but Inrix has provided more than we ever expected," she told me. "There is still so much more that we can do with it, so much more data that's available. so much more awareness. I don't know I could have foreseen that when I was trying to solve the problem," she said. 

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