PORTLAND – Maine’s largest public works project in decades, the $135 million widening of the Maine Turnpike, is just about finished.

The Maine Turnpike Authority will mark the occasion Wednesday by painting a symbolic “final stripe” and opening the new lane on the last remaining section of the state’s busiest highway: the six-mile stretch between Biddeford and Kennebunk.

Some minor landscaping and painting may continue into November, but the paving and major construction are complete.

The project took five years and came in on time and $2 million under budget.

“You want to be joyful the project is over, but in many ways you kind of hate to see it go because it has gone so well,” said Maine Turnpike Authority spokesman Dan Paradee.

“There’s no question the traffic flows so much better now with three lanes,” he said. “It’s a much less congested experience.”

Voters first rejected the widening in a 1991 state referendum, opting instead to explore other ways to reduce and manage traffic. They reconsidered six years later and gave the green light to the plan to widen the 30 miles of the toll road between York and Scarborough from four to six lanes.

Meanwhile, studies of the turnpike highlighted growing congestion and higher accident rates as annual traffic grew from 36.5 million vehicles in 1991 to 44.5 million in 1996.

Many widening opponents from the last referendum now say they are impressed with the results and, in retrospect, many say the project was necessary. But even as they enjoy driving the six-lane road, few say it has changed their original reservations about transportation priorities in Maine.

University of Southern Maine professor Richard Barringer, who opposed the widening in 1997, extolled the improvements in the road but said his concerns remain.

“On the one hand, the road is clearly safer and the Turnpike Authority deserves a great deal of praise. It really looks great,” he said. “At the same time, it will fill up and will continue to generate problems.”

Turnpike engineers have estimated that the widened road will not return to the situation of the late 1990s for another 20 years, but Barringer said he believes gridlock could become a problem again in a decade.