When the state reroutes traffic off a highway under construction, the detour road usually isn't built for it. A new analysis from the University of Minnesota's Center for Transportation Studies puts a number on just how much that costs the roads themselves: in a case study out of Goodhue County, a three-month detour tied to rehabilitation work on U.S. Highway 61 cut more than two years off the remaining service life of an adjacent local road and shrank its effective service area by more than 25%.
Kyle Shelton, the center's director, said the toll is mostly invisible to drivers and easy to overlook in project budgets. He pointed to trucks as the main culprit: "Often particularly trucks because they weigh more put a lot more stress onto our road systems."
The research, led by civil engineering professor Mihai Marasteanu with co-investigator Michael Levin and funded by the Minnesota Local Road Research Board and the Minnesota Department of Transportation, combined field testing with computer modeling. Crews used falling weight deflectometer and ground-penetrating radar equipment on five detour routes and two haul roads around the state, then built a traffic-assignment model to test alternative ways of routing vehicles, especially heavy trucks, during construction.
The upshot: routing trucks more deliberately, even onto slightly longer paths, could cut traffic on the most vulnerable roads by 10% to 15% while still keeping construction-season traffic moving. Tim Andersen, a pavement design engineer with MnDOT's Office of Materials and Road Research, called the resulting framework "a promising starting point" for limiting how much pavement gets used up during a project.
Researchers say the next step is better data — field-measured pavement performance and real-time traffic feedback — to sharpen the model before it's put into wider use planning detours across the state. For U of M engineering researchers, it's a reminder that construction season's costs don't end when the orange cones come down; they show up years later, in local roads that wear out faster than anyone budgeted for.
