Nearly one in ten of the state’s bridges is posted with weight limitations.

Those limits are interfering with the response of some emergency vehicles, and they have forced the Rhode Island Public Transit Authority to reduce service and to abandon some sections of its bus system, including service to two whole towns.

With the Carcieri administration unable so far to find a way to pay for pressing bridge and highway projects, it’s not clear when all of the affected bridges will be repaired or replaced.

Forced to decide which bridges to fix first, the state Department of Transportation has taken a hard-nosed approach that will mean continued disruption and, perhaps, added costs for local governments.

Kazem Farhoumand, the agency’s acting chief engineer, said the DOT doesn’t have a choice.

“We have to make difficult decisions, and we’re making them,” he said. “We don’t have the resources to take care of everything. We need more money.”

As of July 15, 76 of the 772 bridges the DOT says it is responsible for were posted with weight limitations, banned to trucks or restricted to pedestrians — or, in a few cases, closed. The weight limits range from 3 tons up to 18 tons for big highway bridges.

The DOT insists that the limits aren’t forced by safety considerations, but rather by the need to protect the bridges from further pounding from traffic that would speed up their deterioration. The damage is often to steel beams that through rusting have lost enough metal to weaken them, and to concrete piers and beams whose steel reinforcing has rusted, expanded and broken the surrounding concrete.

Most of the DOT’s attention has gone to the big highway bridges, the Sakonnet River Bridge from Tiverton to Aquidneck Island and the Route 95 bridge across the Pawtucket River in that city. Heavy trucks are banned from both, forcing detours.

But most of the posted or closed bridges are in small towns. Foster had the most, eight, followed by Exeter and Burrillville, with seven each. That pattern isn’t new. What has changed is the recent posting of several key local bridges.

Posting is the imposition of a weight limitation by the state Traffic Commission after the DOT, using inspection results, calculates decreased carrying capacity. A sign with a weight limit in tons goes up at the bridge.

Without attention, posted bridges continue to deteriorate, often leading to lower and lower weight limits. In Burrillville, the Shippee Bridge had been posted for 11 tons and then 5 tons. In February, it was reduced from 5 to 3 tons, less than the weight of a loaded, large SUV.

The number of posted or closed bridges has remained at about 80 in recent years. Posted bridges often remain that way — 74 bridges were posted in both April 2004 and this month.

Passenger vehicles generally aren’t affected, although drivers of some large SUVs might want to pay attention. As of July 15, seven bridges were posted at 4 tons or less. Big SUVs, such as the Chevrolet Suburban and the GMC Hummer, weigh more than that when they are loaded, according to the manufacturers’ specifications.

Some bridges will stay posted because they weren’t built to handle present-day loads. The Shippee Bridge, on Route 98 in Burrillville, is posted at 3 tons. But Farhoumand said that truss bridge, built in the 1800s, would be on the posted list even if it were as strong as when it was built.

State law ordinarily limits two-axle vehicles to 22,400 pounds per axle, or 22.4 tons if the weight is distributed evenly. Bigger vehicles are subject to a complicated formula, but the general limit is 40 tons.

In Barrington, the May 15 posting of the Central Bridge, which carries Massasoit Avenue across the Barrington River and is often referred to as the “Bridge at the White Church,” cut the Hampden Meadows part of town off from an important piece of fire apparatus, Fire Chief Gerald Bessette said.

The Barrington fire station is on Federal Road, on the west side of the river. Since the bridge was posted at 15 tons, Bessette said, his engine companies can still cross the bridge, but his ladder truck can’t. It has to go more than a mile south to the Barrington Bridge, cross the river, and make its way back up New Meadow Road or Sowams Road.

Bessette said that the ladder truck is a key part of his department’s response to fires, so “the firefighting operation is definitely slowed down.” He said the delay is from 5 to 10 minutes, depending on where the fire is.

Bessette asked the DOT when the bridge will be replaced.

“Years,” Bessette said he was told.

IT’S WELL KNOWN that the Sakonnet River Bridge, with one end in Portsmouth, is posted because of its rusting steel. But just south of that, the DOT posted Portsmouth’s much smaller Cove Bridge for 10 tons on May 15 after finding that its concrete beams had deteriorated.

Residents call it “the escape bridge,” because it was built to let the 1,300 people in the Island Park neighborhood get out when the other road into the neighborhood, Park Avenue, floods during storms.

Portsmouth Fire Chief Jeffrey P. Lynch said the DOT is allowing his equipment to cross the Sakonnet River Bridge to help out Tiverton — if the fire trucks drive slowly, about 30 miles per hour.

However, he said, the weight limit on the escape bridge “pretty much blocks our access to the Island Park area” if there’s an emergency there during a flood.

THE SAKONNET River Bridge posting in June, for 18 tons, had a sharp impact on truckers, many of whom are forced to a long detour to the Mount Hope Bridge to get from the mainland to Aquidneck Island. It also affected the Rhode Island Public Transit Authority.

“We stopped serving Little Compton and Tiverton,” said RIPTA Assistant General Manager Mark Therrien. That may be a largely symbolic change. Therrien said only a handful of passengers were affected, mainly those using a park and ride lot in north Tiverton.

But elsewhere, he said, many sections of the bus system have been disrupted, and in some cases even abandoned, because of bridge weight limits.

RIPTA Planning Manager Tim McCormick said the posting of the Reservoir Avenue Bridge over the Pocasset River in Cranston forced the authority to split two bus routes into four.

When the DOT posted that bridge and the Pontiac Avenue Bridge early this month, it complicated RIPTA’s operations so much that it took the authority three pages to explain to the public the changes it had to make in its Route 13 (Artic/Washington) and Route 22 (Reservoir/Pontiac) bus lines.

Cranston has lost service to 25 stops, partly because some buses had to be shifted to Route 95, McCormick said.

“It’s a mess,” he said. That was only one of a series of detours and other adjustments RIPTA has made to bridge postings.

The impact on RIPTA has been magnified by the authority’s inability, for lack of money, to add service to compensate for the time lost to detours, authority officials said. That means reduced service somewhere in the bus system. One effect of that is more time between buses, even as drivers are forced to leave would-be passengers behind when buses are full.

ALL THIS makes for tough choices at the DOT, Farhoumand said.

“Every bridge is important to us,” he said, but “we don’t have the resources to take care of everything.”

He said that before posting a bridge, the agency applies several criteria, including the length of detour involved, traffic volume, what kind of road the bridge carries and whether it is “fracture-critical.” That means whether the bridge is subject to sudden collapse if a single element fails.

Costs to local government, while important, aren’t necessarily decisive. In a situation like Barrington’s, he said, “You don’t necessarily have to have a bridge there.

“You can station another fire truck on the other side of the bridge,” he said, “but there are costs involved,” like overtime pay to man the truck.

“It all comes down to dollars and cents,” Farhoumand said. He said replacing the bridge at the White Church is “about three years away.”

blandis@projo.com