LEWISTON — A national transportation research group based in Washington, D.C., has determined that a third of Maine’s bridges are structurally deficient or functionally obsolete.

The group predicted that number would get worse if the state doesn’t start allocating more money for repairs.

The group, called TRIP, announced its findings at a news conference in Portland on Wednesday. The group determined that every bridge in Maine longer than 20 feet has some deficiency.

According to a written statement from the group, 15 percent of Maine’s state and locally owned bridges are structurally deficient, “which means there is significant deterioration of the bridge supports or other major components.”

In Oxford County, 22 percent of bridges are structurally deficient. In Franklin County, the number is 18 percent, and in Androscoggin County, 15 percent.

According to the group, 18 percent of the state’s bridges are “functionally obsolete, meaning they no longer meet modern design standards.” The problem is most severe in southern Maine, where TRIP defined 22 percent of bridges “functionally obsolete.”

In Androscoggin County, 21 percent of bridges are functionally obsolete. In Franklin County, the number is 18 percent, and in Oxford County, 16 percent.

Transportation officials often post these bridges for lower-weight vehicles, restrict or redirect heavier vehicles — including school buses and emergency vehicles — and close bridges in some cases.

According to TRIP, while the number of Maine bridges that are deteriorating is on the rise, “the number and share of structurally deficient bridges in the U.S. is decreasing.”

One of the reasons Maine is seeing its bridges tire is because of increased vehicle miles traveled since 1990. According to TRIP’s findings, vehicle miles traveled in Maine in 1990 were 11.9 billion. By 2013, that had increased to 14.1 billion, a 19 percent rise.

By 2030, TRIP predicts, vehicle miles traveled in Maine will increase another 15 percent, creating greater strain on bridges.

Some of the structurally deficient bridges TRIP has identified in southern Maine include the Route 1 bridge over Cousins River in Freeport, and the bridge that carries Routes 11 and 114 over the Muddy River in Naples, both of which were built in 1930.

The group also identified the bridge that carries Routes 9 and 22 over the Stroudwater River in Portland as deficient. That bridge, which carries 23,826 vehicles per day, was built in 1989 and is among the youngest bridges in Maine.

A number of bridges built in 2014 were also classified as structurally deficient and in poor condition, according to TRIP, including the Cumberland Street bridge over the Presumpscot River in Westbrook. The bridge carries 16,234 vehicles per day and its decking and substructure are in poor condition, with the superstructure classified just slightly higher.

TRIP also lists the Center Bridge Road bridge over the Androscoggin River in Turner as structurally deficient. Built in 2014, it carries 2,470 vehicles a day and its decking is in poor condition.

Among the lowest ratings were the Route 1 bridge over the Saint John River in Fort Kent. Built in 1929, the decking and superstructure are in very poor condition. TRIP calculated that 955 vehicles travel that bridge every day.

The North Elm Street bridge in Yarmouth, built in 1953, was also listed in very poor condition, as was the Cobbs Bridge Road in New Gloucester, built in 1934. Both bridges cross the Royal River. They carry 2,869 and 511 vehicles per day, respectively, according to the TRIP report.

The McNeil Road Bridge over the Old Course Saco River in Fryeburg is classified as having the worst decking of any bridge in Maine. Its substructure is listed in poor condition, but its superstructure is rated very well. That bridge is closed, according to the TRIP report.

The Route 126 bridge over the Sabattus River in Sabattus is listed as one of the better bridges in Maine. It was built in 1951.

Other bridges that scored well were the Mill Hill Road bridge over Martin Stream in Turner, the Bridge Street bridge over the Maine Central Railroad tracks in Lewiston, the Route 145 bridge over Valley Brook in Strong, the Routes 2, 5 and 26 bridge over the Androscoggin River in Bethel, and the Route 35 bridge over the Crooked River in Waterford.

In its report, TRIP researchers determined that “meeting Maine’s need to modernize and maintain its system of roads, highways and bridges will require a significant boost in local, state and federal funding” to upgrade bridge conditions.

In reaching its findings, TRIP relied on information provided by the Maine Department of Transportation, the Federal Highway Administration, the National Bridge Inventory, the U.S. Census Bureau and the Bureau of Transportation Statistics.

Researchers have recommended that Maine modernize its transportation system by improving the condition of its bridges, something that will create jobs in the short term and stimulate “long-term economic growth as a result of enhanced mobility and access” for private and commercial vehicles.

At the news conference in Portland, Maine Chamber of Commerce President Dana Connors said every business in Maine depends on the state’s transportation system.

“It is critical that we increase the investment in our bridges, first and foremost for the safety of the traveling public, but also for the many businesses across Maine that depend on our system to ship their products to market,” he said in a written statement.

For more information, including the full list and rankings of Maine bridges, go to tripnet.org.

Preserving Maine’s Bridges: The Condition and Funding Needs of Maine’s Bridge System

Highlights from the TRIP report identifying deficient bridges in Androscoggin, Franklin and Oxford counties:

Auburn: Cedar Street bridge over the Androscoggin River. The bridge, built in 1936, carries 14,624 vehicles per day. The substructure and the superstructure are in poor condition.

Auburn: Oakdale Bridge over the Little Androscoggin River. The bridge, built in 1931, carries 8,385 vehicles per day. The superstructure is in poor condition.

Fryeburg: Route 302 bridge over the Saco River overflow. The bridge, built in 1931, carries 3,296 vehicles per day. The decking and superstructure are in poor condition.

Leeds: Church Hill Road bridge over Allen Stream. The bridge, built in 1941, carries 770 vehicles per day. The substructure is in poor condition.

Lewiston: Interstate 95 bridge over the Alfred Plourde Parkway. The bridge, built in 1956, carries 4,380 vehicles per day. The substructure is in poor condition.

New Sharon: Route 41 bridge over McGurdy Stream. The bridge, built in 1931, carries 1,040 vehicles per day. The substructure is in poor condition.

Oxford: Route 121 bridge over the Little Androscoggin River. The bridge, built in 1940, carries 4,870 vehicles per day. The decking and substructure are in poor condition.

Peru: North Main Street bridge over the Androscoggin River. The bridge, built in 1930, carries 5,270 vehicles per day. The superstructure is in poor condition.

Rumford: Route 2 bridge over the Swift River. The bridge, built in 1952, carries 9,850 vehicles per day. The decking and superstructure are in poor condition.

Rumford: Route 2 bridge over the Ellis River. The bridge, built in 1928, carries 4,108 vehicles per day. The decking and substructure are in poor condition.

Turner: North Parish Road bridge over the Nezinscot River. The bridge, built in 1941, carries 3,320 vehicles per day. The decking is in poor condition.

Wilton: Routes 2 and 4 bridge over Wilson Stream. The bridge, built in 1962, carries 9,360 vehicles per day. The decking is in poor condition. The superstructure and substructure are rated in much better condition.