Tolls starting at 18 cents a mile could pay from one-quarter to one-half of the more than $3 billion price tag to complete Interstate 49 South from Lafayette to New Orleans, according to a state-funded feasibility study unveiled Monday.

Discussions of tolls are in the early stages, but advocates for pushing forward I-49 South said the study shows that a mix of toll revenue with federal and state money could pave the way for the road.

“Tolls are probably going to have to be an integral part of getting I-49 done, as long as people are getting what they are paying for,” said state Sen. Bret Allain, R-Franklin, the main force behind the recent formation of the I-49 South Coalition, a group of politicians, business owners and economic development officials trying to push the project forward.

Allain and others said they were disappointed Monday that the feasibility study didn’t find the toll revenue could pay for a bigger chunk of I-49 South.

“We realize this is not necessarily the best of news,” said Dennis Decker, assistant secretary of multimodal planning for DOTD.

The numbers should not be discouraging, said Michael Copeland, a planner with consultant CDM Smith, the company that did the toll feasibility study.

“It’s very rare for a facility nowadays to completely pay for itself,” he said.

The toll study looked at the financial feasibility of tolling the entire 145-mile stretch from Lafayette to New Orleans or tolling only segments within that stretch, with tolls collected in each segment supporting work only in that segment.

The study found that tolls collected along the entire 145-mile route could pay from 26 percent to 51 percent of the project.

The numbers were similar — 27 percent to 53 percent — if tolls were collected only on the portion from I-10 stretching 59 miles south to the Wax Lake outlet.

The figures looked better for a 50-mile stretch about midway between Lafayette and New Orleans — toll funding could pay for 54 percent to 106 percent of the project — but most of that portion is already complete.

The study assumes tolls starting at a rate of 18 cents a mile and rising over 15 years to 25 cents a mile.

DOTD has done several projects in recent years that have brought much of U.S. 90 up to interstate standards.

The big-ticket items that remain include the portion of the interstate near New Orleans and the elevated I-49 Connector through Lafayette, which is estimated at more than $700 million.

It seems unlikely a project of that magnitude will be built without the help of toll dollars, said Mike Michot, a former state senator serving as director of the I-49 South Coalition.

“We are finding that more of the stakeholders are open to tolls as a viable option,” Michot said.

Allain said any toll proposal would need to focus not on the entire stretch from Lafayette to New Orleans but on areas where upgrades are still needed, because drivers likely will not want to pay tolls in areas where U.S. 90 already meets interstate standards, which it does in large sections of St. Mary and Iberia parishes.

“Politically, it’s going to be a very big challenge,” he said.