The first scenario is based on an average toll rate of 4 cents a mile; the second, an average rate of 12 cents a mile. The range of rates is comparable to other states, such as Illinois, that collect highway tolls, according to the study.

Under the same scenarios, a trip from Madison to La Crosse would cost as little as $5.16 or as much as $15.48.

Even if state leaders could agree on a toll-road plan — which is far from assured — another big hurdle would be getting federal permission to toll U.S. interstates, where the most revenue could be generated.

The study notes that a 2015 change in federal law might allow Wisconsin to vie with other states for spots in a federal pilot program to authorize interstate tolling.

Wisconsin’s transportation-funding woes stem from rising construction costs and stagnant revenues in the state transportation fund, which come almost entirely from gas taxes and vehicle registration fees. As the state’s road-funding picture has worsened in recent years, lawmakers increasingly have resorted to greater borrowing and delaying major highway projects, such as the Verona Road expansion in Dane County.