UA Engineers to Help Ease Traffic Woes Following Minneapolis Interstate Bridge Collapse

Ed Stiles
Aug. 3, 2007

The Federal Highway Administration has asked Assistant Professor Yi-Chang Chiu to use an urban traffic simulation model developed at The University of Arizona to help in rerouting traffic in Minneapolis following the collapse of the IH-35W Bridge.

Seventy percent of the traffic through the collapsed IH-35W Bridge is downtown-bound, and the bridge carries more than 140,000 cars daily.

Rerouting traffic requires an accurate prediction of traffic movements within the city, said Chiu, of UA's Civil Engineering and Engineering Mechanics Department.

Within the next several weeks, Chiu's team will develop a traffic simulation model for the entire cities of Minneapolis and St. Paul. The researchers then will use the model to simulate and evaluate a selected number of mitigation strategies approved by the Minnesota Department of Transportation (MnDOT) and the Federal Highway Administration (FHWA).

The UA team expects to work closely with MnDOT and FHWA throughout the bridge rebuilding process, which may be as long as two years.

Chiu has been developing the traffic simulation software since 1995, when he was a graduate student at the University of Texas in Austin.

"Solving large-scale problems like this one is overwhelming without a sophisticated simulation package," Chiu said. "No one can just sit down with a map and draw lines and figure out the best answer to problems like these."

The software package depends on detailed traffic census and planning data that is collected by state and city transportation agencies in conjunction with real-time traffic surveillance data.

The team will first determine the origins and destinations of commuters throughout the day.

"Drivers will select a route that results in acceptable travel time," Chiu said. "If drivers choose a congested route today, they will probably try another route tomorrow until they find a satisfactory route." Hundreds of thousands of drivers will be making similar decisions, collectively affecting every other driver's travel time.

The software simulates the day-to-day learning process for each driver and collectively estimates the traffic conditions for the entire city. The software also describes how commuters may respond to various traveler information sources such TV news, Web sites, radio broadcasts or message bulletin boards along major freeways.

FHWA or MnDOT will use the model to evaluate several mitigation strategies, including rerouting traffic through other corridors or highways and re-timing traffic signals to accommodate traffic flow patterns that are now different from what the timing was originally designed for, Chiu said.

"The main emphasis of the analysis is the integrated corridor management concept that focuses on multi-modal solutions in which all the possible transportation modes are coordinated," he said. "This includes transit and buses, value pricing and intelligent transportation systems (ITS) technologies."

Chiu has worked with the following agencies on developing and testing the software: Federal Highway Administration, Oak Ridge National Laboratory, Arizona Department of Transportation, Texas Department of Transportation, Florida Department of Transportation, CalTran, Virginia Department of Transportation, Maricopa Association of Governments, Pima Association of Governments, the Harris County in Houston, and the El Paso Metropolitan Planning Organization.


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Yi-Chang Chiu
Assistant Professor
Civil Engineering and Engineering Mechanics