Authority board of directors, on Thursday, approved a 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 Larabee Road exit in Portland.

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 keeps seeing 3 percent annual traffic growth, the section of highway will be “stop-and-go-” traffic at peak travel times within seven years, Godfrey 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 over the next seven years.

Turnpike authority staff also intend to coordinate with regional transportation planning and public transit agencies to explore measures that can reduce future congestion, such as more carpooling and an express public bus for the Turnpike between Biddeford and the Portland area.

It hopes to begin applying for construction permits by the end of the year.