Findings from the study, commissioned by state lawmakers and Walker last year as part of the 2015-17 state budget, were released Wednesday. A day earlier, Transportation Secretary Mark Gottlieb, with little explanation, announced his resignation effective next month.

Walker’s office did not immediately respond Wednesday to a request for comment on the study.

The question of how to address state transportation funding is expected to feature prominently in the upcoming 2017-18 legislative session.

Assembly Republican leaders say toll roads, which currently don’t exist in Wisconsin, should be considered.

The DOT study does not recommend for or against tolling, but gives a broad overview of its pros, cons, and of how it would be implemented.

Any plan for toll roads would take at least four years to implement, the study found. It estimates upfront capital costs for tolling Wisconsin’s interstates would range between $350 million and $400 million.

The study assumes highway tolls would be collected electronically — via transponders in vehicles or by photographing vehicle license plates and mailing toll bills to vehicle owners. Such a system eliminates the need for motorists to stop to pay a toll, and for toll plazas that restrict highway access.

Depending on the chosen toll rate, the state could net between $14 billion and $41 billion from tolling on interstates from 2020 through 2050, the study found. The numbers are based on a statewide network of tolls that would be collected on all Wisconsin’s U.S. interstates: 94, 90, 43, 41 and 39.

The revenues would come from motorists, including in- and out-of-state residents. The study attempts to project the share of motorists who would avoid interstates to dodge the tolls.

Under the study’s projections, a motorist would pay between as little as $2.72 or as much as $8.16 to travel from Madison to Milwaukee.

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.

Assembly Speaker Robin Vos, R-Rochester, and fellow Republicans who control the Assembly are open to a tax or fee hike for transportation. Walker opposes such an increase unless matched, dollar for dollar, with a tax or fee cut elsewhere in the budget. Republicans who control the state Senate are split on the question, according to their majority leader, Sen. Scott Fitzgerald, R-Juneau.

The new study reinforces what Gottlieb told the Assembly Transportation Committee earlier this month: without new revenues, more projects would be delayed and the state’s roads would continue to crumble.

On a path following the plan Walker outlined in September, the state would face a transportation funding shortfall of $852 million over the decade, the study found.

Road conditions would worsen “severely” during the next decade, according to the study. And planning for road expansions would grind to a halt, with planning for them not even undertaken until 2055.