Henry Liu: Developing Smarter Stoplights

It’s probably safe to say that drivers have cursed sitting in line at stoplights ever since the nation’s first electric traffic light was installed in Salt Lake City, Utah in 1912.

Since then, traffic managers have learned how to time lights to smooth the flow of traffic on busy arterial highways. But because traffic data for these kinds of roads is rarely stored or analyzed, traffic rarely moves as fast or as smoothly as it could.

However, now traffic managers have a way to economically record traffic movement. A University of Minnesota scientist has devised his SMART Signal system to measure queue length and traffic speed at stoplights and to analyze it—all without a lot of expensive add-on equipment. The result is a new startup company SMART Signal Technologies that is beginning to market the technology to counties, cities, and other transportation managers to speed traffic and reduce congestion on major roads and highways with signals.

The benefit to drivers—less aggravation, fewer delays, and reduced fuel consumption. “There are all sorts of reasons we have to operate our traffic lights efficiently,” said Henry Liu, the assistant civil engineering professor in the Center for Transportation Studies who developed SMART Signal.

Until now, says Liu, “how we evaluated traffic signal performance has been largely manual effort.” Someone sits at an intersection, counts the number of cars that stop in the queue and times how long they remain at a standstill. Government has to pay someone to do that, and then it has data only for the brief period it sent someone to count cars.

"There are all sorts of reasons we have to operate our traffic lights efficiently."

— Henry Liu

That was state-of-the-art several years ago when the Minnesota Department of Transportation sent out a research request for a means to evaluate traffic signal performance using existing infrastructure. “I thought that was an interesting topic,” Liu said.

The “existing infrastructure” of a light-controlled intersection is pretty basic: The light itself. A detector such as an inductive loop imbedded in the roadway near the intersection, and a controller cabinet with circuitry to change the duration of the light when traffic starts to pile up.

To develop his system, Liu installed a laptop computer inside the controller cabinet to receive the information the controller receives about signal timing and passing cars. Liu then developed two algorithms to analyze this data. One estimates queue length. The other estimates travel times through a particular stretch of highway.

“That is very important information for traffic engineering purposes,” Liu said. “It is also important for drivers. If I post this information online, you will be able to see which intersection is congested so you can make the decision you want to avoid that intersection. And if you want to go from point A to point B you can actually estimate your travel time.”

Most importantly, the SMART Signal analysis lets traffic managers know what is happening at their signals, 24/7.

“If we know what’s going on, we know what to do,” said Liu. “Once you know the performance, fine tuning the signal parameters is a lot easier.”

Liu has been testing his SMART Signal system on several highways in Minnesota and California, including Highway 55 in Golden Valley, France Avenue in Bloomington, and Highway 13 in Burnsville. The Minnesota Department of Transportation, Minnesota Local Road Research Board, the University’s Intelligent Transportation Systems Institute, Hennepin County, and the National Cooperative Highway Research Program have provided funds for his research.

SMART Signal Technologies, launched in late 2011, is offering the new technology to highway managers—basically, any city, county, or state. “Anyone who has traffic signals to manage is a potential customer for us,” Liu said.