More accurate traffic modeling could improve planning for construction projects
Construction on Twin Cities freeways gives drivers plenty of chances to try alternative routes—and sometimes, find that those routes are under construction, too. In a project funded by the Minnesota Department of Transportation (MnDOT), U of M researchers evaluated the capabilities of simulation software packages that could be used to improve construction project staging and, ultimately, help minimize disruption from overlapping projects in a region.
“Traffic modeling is a valuable transportation planning tool for predicting the impacts of new construction or maintenance projects,” says John Hourdos, director of the U of M’s Minnesota Traffic Observatory and the project’s principal investigator. “However, it is often only available in two scales: microscopic or macroscopic.”
Microscopic-scale traffic simulation emulates real-world conditions, including behaviors such as acceleration rates, but it isn’t feasible for inter-corridor or regional analysis because of the large amount of data and computing power required. Macroscopic-scale planning tools predict driver route choice and travel demand, but only for static traffic conditions.
To bridge these two scales, MnDOT is developing a mesoscopic, traffic-simulation-based, dynamic traffic-assignment model for the Twin Cities. “Large-scale mesoscopic traffic simulation is a newly adopted tool made possible by recent advancements in traffic modeling and computer hardware,” Hourdos says. “A mesoscopic model can be used to stage construction seasons to minimize the disruption caused by multiple large projects or to coordinate traffic modeling across the road networks operated by the state, counties, and cities.”
For the project, researchers evaluated the capabilities of currently available simulation software packages to meet MnDOT’s needs. “Dynamic traffic assignment is an emerging methodology, and there are a lot of software platforms with different implementations,” says Jim Henricksen, traffic forecaster with MnDOT’s Metro District. “MnDOT was interested in reviewing their pros and cons.”
Investigators interviewed stakeholders who have used or requested traffic simulation information about their understanding of and need for mesoscopic traffic simulation. In addition, they reviewed four case studies of mesoscopic simulations used in Manhattan, San Francisco, Detroit, and Jacksonville, Florida. Next, they conducted a comprehensive review of six commercially available traffic simulation software packages to identify limitations of their methods and whether those methods are applicable to MnDOT’s needs.
To compare the capabilities of the simulation software packages, the team created a compatibility matrix that identifies dozens of components necessary for accurate models, then analyzed how each of these features are handled by the different software systems. “Our matrix produced some interesting insights: for example, some software packages claim to model actuated signals, but they create models based on assumptions rather than real-world conditions,” Hourdos says.
Based on the results of this effort, researchers identified two software packages—TransModeler and AIMSUN—that stood out from the rest. Then, they leveraged significant pro bono work from the software developer to build out and test the foundation of a mesoscopic model for the Twin Cities in TransModeler.
“Our findings lay the groundwork and procedures for MnDOT or other agencies to create a mesoscopic-scale traffic modeling system for the Twin Cities,” Hourdos says. “Moving forward, MnDOT can use the information gathered in this project to determine which approach is more practical for the agency and its consultants based on cost, capabilities, and data availability.”