Highway construction is a sign of progress on Minnesota’s roadways. Unfortunately, construction detours often create problems for local roads designed for light traffic but forced to accommodate heavy freight trucks. Although counties are reimbursed for this usage, the current compensation models rarely cover the true structural toll. As a result, local roads are often left “consumed” long before their intended expiration date.
Examining the structural and economic impacts of detours was the focus of a new study led by CTS scholar and University of Minnesota Civil, Environmental, and Geo- Engineering Professor Mihai Marasteanu. The project was sponsored by the Minnesota Local Road Research Board and Minnesota Department of Transportation (MnDOT).
“Our ultimate goal for this project was developing a framework for optimizing detour routes that limit pavement damage while maintaining traffic mobility,” Marasteanu says.
To gain a more nuanced understanding of the actual toll of detours on a local road’s health, the research team examined impacts through two lenses:
- Remaining service life, focusing on how much sooner a road will reach its “failure” point as a result of the accelerated aging caused by heavy loads.
- Effective service area, using a more holistic metric to measure the total “amount of service” or ride quality a road provides over its lifetime.
Both methods used a comprehensive set of performance curves developed by the Pavement Management Office at MnDOT, which takes advantage of the extensive reconstruction and rehabilitation historical data available in MnDOT’s Highway Performance Management Application database.
A case study of a road in Goodhue County, Minnesota, demonstrated the significant impact of detours on local roads. In just three months of use as a detour for a U.S. Highway 61 rehabilitation project, the local road lost two years of service life and saw a 25 percent reduction in its effective service area.
“This means the road just didn’t get older,” Marasteanu explains. “It lost a quarter of its ability to perform its job long before its time.”
To help prevent this kind of rapid decay, investigators developed a tool that uses genetic algorithms to design an optimal detour route. The tool simulates how cars and trucks behave during a closure and creates a routing plan based on thousands of trials. By identifying which local links are the most vulnerable, the model maps routes that minimize truck-related impacts while keeping traffic flowing. In simulations, the model successfully reduced truck flows on vulnerable roads by 10 to 15 percent.
To put these findings into practice, researchers developed a five-step framework for mitigating detour impacts:
- Collect essential network data such as rehabilitation history, performance curves, and pavement layer thickness.
- Quantify pavement consumption by using the remaining service life or loss of area (e.g., holes or other areas of missing pavement) to quantify the damage.
- Optimize detours by leveraging models to select the “smartest” route, not just the shortest.
- Simulate and test detours virtually before real-world implementation.
- Validate and compare predicted traffic with real-world reductions to refine plans.
“This framework represents a promising starting point to map detour routes that will minimize pavement consumption on the available local network,” says pavement design engineer Tim Andersen with MnDOT’s Office of Materials and Road Research.
While the researchers note that better data on local road structures is still needed, this project provides a foundation for a more equitable system. By moving toward a “traffic-aware” detour strategy, Minnesota can ensure that fixing its highways doesn’t come at an unfair cost to local road networks.
—Megan Tsai, contributing writer
