AUGUSTA, Maine — The condition of Maine’s roads, bridges, airports and other infrastructure has barely budged in the past four years, highlighting the need for a long-term and sustainable funding stream for infrastructure improvements.

That’s according to a new report card from the state’s affiliate of the American Society of Civil Engineers. Overall, the organization gave Maine’s infrastructure a C-, unchanged from the grade the state received the last time the group published a report card in 2008.

The group unveiled its 2012 report Thursday at a state transportation conference.

“This report is a call to action to improve our quality of life here in Maine,” said Will Haskell, president of the Maine section of the American Society of Civil Engineers and vice president of Gorrill-Palmer Consulting Engineers in Gray.

The report card evaluated 14 categories of Maine’s infrastructure, from the quality of municipal drinking water systems and solid waste facilities, to the condition of the state’s ports and waterways, to the way the it handles the cleanup of contaminated sites.

Maine earned its highest marks this year for the condition of its airports. The state received a B in that category, up from a B- four years ago. The state received its lowest grade, a D, for the condition of its roads. That grade didn’t change from the 2008 report, though the report noted that some conditions improved during the past four years as a result of temporary federal funding.

Some 38 percent of the state’s major roads are in fair condition or worse, according to the civil engineers’ group.

“Our infrastructure system is the very foundation of our way of life, but continues to be neglected,” Lauren Swett, vice president of the group’s Maine section, said in a statement. “Maine’s infrastructure is struggling to meet the public’s needs, and challenges such as underinvestment have left the state susceptible to falling behind.”

The infrastructure report card is the result of 19 Maine civil engineers’ review of hundreds of public records over the past year.

This year’s report card was released about a month after voters signed off on nearly $60 million in borrowing to fund infrastructure improvements in a number of the 14 categories rated by the civil engineers. Voters approved a $51.5 million bond issue to fund improvements for highways, bridges, airports and ports at Searsport and Eastport. They also supported a measure to direct $7.9 million toward drinking water systems and wastewater treatment facilities.

While voters have signed off on the borrowing, it’s unclear when the state will have the money on hand and when the work will begin. Gov. Paul LePage has said he doesn’t plan to issue bonds until he’s able to rein in state spending.

The report’s release also came days after the state’s Revenue Forecasting Committee revised revenue projections for the Highway Fund downward for the coming two-year budget cycle. The forecasts now predict highway revenues during the next two years — which come primarily from the state fuel tax — will fall $20.3 million short of earlier estimates.

Conventional sources of funding for the state’s roads — namely the gasoline tax — aren’t producing the needed level of funds, said Maine Transportation Commissioner David Bernhardt.

“People are driving less. People are driving more fuel-efficient cars,” he said. “We’ve got to figure out another source of funding.”

And that funding source is unlikely to be additional transportation bonds, especially for regular road improvements, Bernhardt said. Even if LePage releases transportation bond funding earlier than expected, it won’t make much of a difference in solving the state’s highway funding problem, he said.

“Bonding is just short-term, and you’ve got to pay it back,” Bernhardt said.

Maine’s 2012 grades improved from 2008 in five categories: contaminated site cleanup (D+ to C-), municipal drinking water (C to C+), airports (B- to B), bridges (D+ to C-), and ports and waterways (C- to C+).

The state’s 2012 grades were unchanged in seven categories: roads (D), railroads (C), dams (D+), energy infrastructure (C+), municipal wastewater (D+), passenger transportation (C-) and schools (C-).

While grades stayed the same, the civil engineers’ report noted progress in the roads, railroads and energy infrastructure categories. The report noted backwards movement in passenger transportation due to the condition of Maine’s public transit vehicles.

Maine’s grades fell in two categories: solid waste (C to C-) and state parks (B- to C+).

Bernhardt said the state is making progress on road projects and seeing progress in other areas, including the expansion of Amtrak passenger rail service to Brunswick. The Maine Department of Transportation is also developing a grading system of its own for the state’s roads.

“I can’t tell from the [civil engineers’ society] report card if I’m moving the needle,” he said. “I have to know how much we’re moving the needle.”

Maine’s report card is modeled after the American Society of Civil Engineers’ nationwide infrastructure report card. The most recent report, in 2009, gave the nation’s infrastructure a D.