The Maine Turnpike Authority will move quickly to widen part of the four-lane highway in the Portland area.

The authority’s board of directors on Thursday approved a scaled-back plan to add a travel lane in each direction to about 5 miles of the turnpike, which is Interstate 95, from Scarborough to about a mile beyond the Larrabee Road exit in Portland. The original plan called for widening about 9 miles of the highway.

Besides adding more roadway, the plan includes replacing three bridges and modifying several others, redesigning the Exit 45 interchange in South Portland and improving medians. The estimated cost is $140 million to $160 million, said turnpike authority Executive Director Peter Mills said. Construction is expected to start next year and wrap up by 2022.

“This is coming at an opportune time because bridges on this route need some sort of serious attention,” Mills said.

The project will be paid for through a $173 million capital improvement bond the authority took out this year.

Widening the turnpike in this area has been considered for more than a decade, but steadily growing highway traffic makes the project more urgent, said Paul Godfrey, a traffic engineer from HNTB Corp., the engineering company that conducted a study of demand and capacity for the authority.

If the turnpike continues to see 3 percent annual traffic growth, the section of highway will have “stop-and-go” traffic at peak travel times by 2025, Godfrey said.

“We are fully aware that if this trend continues, the need to address the issue becomes more urgent,” he said.

Turnpike officials envisioned widening the highway for about 9 miles, from Exit 44 in Scarborough to Exit 53 in Falmouth. But since traffic volume and congestion falls sharply after the last exit in Portland, it will instead expand the southern section first and monitor traffic on the remaining 4 miles.

The turnpike was widened to three lanes from the New Hampshire border to Scarborough between 2000 and 2004. The authority planned to extend the three-lane highway about 10 years ago, but shelved plans after the onset of the Great Recession.

With traffic surging back onto the highway causing traffic jams and more crashes, turnpike officials decided it was time to revisit the plan.

In the short term, drivers are likely to experience construction delays because of the widening project and two others being undertaken during the same time frame – a $30 million project to resurface the Piscataqua River Bridge and a $40 million plan build a new toll plaza in York.

MITIGATING CONGESTION

More than a year ago a public advisory committee started examining options for reducing congestion and improve safety on the congested section of the turnpike. Ideas included more regional and municipal transit, passenger and freight rail, adding tolls to reduce congestion and more carpooling.

Committee members evaluated 19 alternatives in all, Godfrey said. Some showed promise, but were either unfeasible or not cost-effective.

“While 14 partially met the study purpose, they only solved a small-to-medium part of the problem,” he said. Adding travel lanes to the turnpike “met the study purpose, was cost-effective and could be realized in a reasonable amount of time,” he said.

Widening the highway is presently the most effective way to resolve looming congestion and safety problems, but the authority wants to collaborate more with regional transportation and public transit agencies to mitigate future problems, Mills said.

Part of the resolution the board approved Thursday directs the authority to bring the board “any reasonable, effective and prudent measures to preserve the traffic capacity of the turnpike and to further improve mobility within the region served by the Portland widening project.”

OTHER AVENUES PURSUED

Transportation management programs such as the Go Maine ride-sharing program managed by the turnpike, park-and-ride lots and working with targeted employers to reduce peak-hour trips to and from Portland are among the ways the Turnpike can play an active role, Mills said.

“It is part of the DNA of this organization to provide mobility services that are not necessarily just taking tolls,” he said.

The authority also could provide initial funding for an express public bus route on the turnpike between Biddeford and Portland. The idea for a express bus came from the advisory committee’s analysis and shows promise to reduce the number of vehicles on the road.

“A preliminary expectation from the study is that it should work,” Mills said.

No groups have emerged in direct opposition to widening the turnpike. However, members of the public advisory committee and the Conservation Law Foundation have urged the authority to carefully consider other alternatives before committing to new road construction.

Others have pointed to research that indicates the volume of traffic grows as more capacity is added, ultimately negating the benefit of added travel lanes.

Sean Mahoney, director of the Conservation Law Foundation’s Maine Advocacy Center, told the board his group felt “the need for widening the turnpike has been made evident.” The board should evaluate if more lanes will be needed after more capacity is added to the Portland area, he said.

“We would urge you to do an assessment after the first phase to see if the changes that have been made have made an impact.”