Details about a long-planned project to widen the Maine Turnpike between South Portland and Falmouth show that some parts of the heavily traveled highway will exceed capacity within seven years.

That information comes from a citizen advisory committee charged with looking at alternatives to ease congestion on the 11-mile stretch of highway. If unchanged, rush-hour traffic would be at a standstill around most exits by 2040, according to a draft report of the study.

The committee studied 15 options to deal with future congestion, and concluded that expanding the four-lane highway to six lanes was the only way to fully address the issue. A complete report is expected in July.

Turnpike widening will cost at least $142.7 million, the committee estimated. About $57 million has been allocated in the turnpike’s four-year capital plan for work on four bridges that need to be modified before the highway is expanded.

“It has always been in the long-range planning that we would have more lanes on this part of the highway,” Peter Mills, the Maine Turnpike Authority’s executive director, said in an interview Tuesday.

“The traffic we are seeing on too many occasions is really congesting the mainline,” he added. Turnpike traffic has been setting monthly records since 2016.

“There is no immediate sign of any slowdown in growth,” Mills said.

Turnpike officials will present findings from the yearlong study to municipal executives in Portland, Westbrook, South Portland and Scarborough in coming weeks.

Members of the public will get a chance to look over the findings and offer suggestions at a public forum at the Maine Mall on Thursday from 4:30-6:30 p.m.

The committee considered alternatives that included adding public rail and bus transportation, carpooling, reversible lanes, congestion pricing, and widening and creating toll on I-295.

A study of alternatives was required by a 2007 state law and will be used to apply for a construction permit from the U.S. Army Corps of Engineers.

However, the process was more than just a legal exercise, Mills said.

“It may boil down to the fact that we do need to widen the highway and do it very soon, but that doesn’t mean there aren’t also things that should be done in the future,” he said.

“One of the concerns people going to the committee meetings have is, if you build a wider highway, how do you make sure it remains useful without encountering more congestion later?”

The turnpike planned to widen the same part of the highway about a decade ago, but dropped the plan after traffic dipped during the Great Recession that began in December 2007.

Turnpike officials expect to apply for construction permits by the end of the year, Mills said.

Work will include modifying four bridges over and on the highway, starting this fall with the Cummings Bridge in Scarborough near the Maine Mall.

Construction will take place before the Turnpike starts on a proposed highway spur from Gorham to the Maine Mall to ease traffic in Portland’s western suburbs.

“You would not build a Gorham connector and bring more traffic into a situation where you already have congestion problems,” Mills said.