PROVIDENCE — The state Department of Transportation yesterday reduced the weight limit on the Route 95 bridge across the Pawtucket River for the second time because continued deterioration of major structural elements has further reduced its capacity.

Kazem Farhoumand, the DOT’s acting chief engineer, said that the bridge remains safe and that the weight limit, reduced to 18 tons from 22 tons, has been changed to head off more deterioration, not because of a threat of collapse.

“If a truck that’s 19 or 20 tons goes over it, it doesn’t mean it’s going to cause major damage,” he said. He also said the DOT may repair the beams whose deterioration prompted the new weight limit.

Farhoumand said the reduction is in response to inspection results received last week that found increased deterioration of three steel floor beams. DOT officials met Tuesday with agency consultants and Federal Highway Administration officials and decided to impose the new weight limit, he said.

Farhoumand said it’s possible that some loaded school buses might reach the new limit, and in that case, “I would take the detour.” He offered to arrange to have buses weighed by the state police, who enforce the weight limit, if school officials want, “to put everybody’s mind at ease.”

John DiTomasso, assistant administrator at the state Division of Motor Vehicles, said he thinks it’s “highly unlikely” that school buses will exceed the 18-ton limit, and that relatively few school buses use the bridge. Also, he said, some models are lighter than others. If buses approach the limit, he said, school transportation officials can probably use lighter bus models for field trips to Boston, for example, rather than take a detour.

The bridge is actually two separate bridges, one carrying northbound traffic and the other southbound. Their superstructures are based on four steel main girders running parallel to traffic, one at each edge of each of the bridges. The floor beams, 35 on each bridge, run between the main girders, perpendicular to traffic.

Other, smaller beams run lengthwise on top of the floor beams and directly support the concrete deck.

David W. Fish, the DOT’s managing engineer for bridge engineering, said that two of the problem floor beams are on the southbound side, and that the inspection showed their capacity reduced to 18 tons. The other one, on the northbound side, is rated at 20 tons, he said.

Farhoumand said that having trucks heavier than the weight limit cross the bridge won’t cause an immediate problem. The trouble, he said, is that “if people continue doing that, over time it’s going to cause more damage,” reducing the bridge’s capacity and causing events like yesterday’s.

The DOT’s strategy, officials have said, is to keep inspecting the bridge, respond to problems as they emerge, and try to keep it operating at an acceptable capacity as cheaply as possible until it can be replaced.

“We hope to get out there sometime next year to start the replacement,” Farhoumand said yesterday.

He said the current problems don’t apply to the bridge’s categorization as being “fracture-critical.” The term applies to the Pawtucket bridge because the failure of any of the four main girders could cause a collapse, since that would leave one edge of the deck entirely unsupported. But Farhoumand noted that the bridge’s immediate problems don’t affect those girders. The floor beams that are the problem are spaced more closely, 30 feet apart, and the failure of one of them wouldn’t cause a collapse, he said.

On the other hand, the bridge has many serious problems that the DOT has already made public, including beams with holes rusted through them, sections of beams entirely rusted away and a deck that sounds hollow when you hit it in some places. That suggests that the concrete is coming apart, according to an inspection report the DOT made public in December.

When it first imposed a weight limit in November, the DOT also permanently closed a northbound entrance ramp onto the bridge, installed steel brackets to help support the far-right lane northbound where it forms the deceleration lane for the School Street exit and installed a temporary steel column to help hold up that section of the bridge. It also shifted traffic away from the bridges’ edges in both directions.

The DOT has also asked the General Assembly for authority to ban all vehicles with three or more axles. It said that’s needed because overweight trucks continue to use the bridge despite the weight limit and because of the difficulty of enforcing a limit that affects many trucks when they are full but not when they are empty. Where imposing a significant fine now requires weighing a truck to prove it is overweight, it’s easy to see how many axles a vehicle has.

Farhoumand said that he does not expect a large impact on truck traffic, and that the detours, routed through city streets when the DOT imposed the weight limit in November, are working well. The DOT has also been directing through truck traffic around the bridge, using routes 146 and 295.

Built in 1958 as part of the original interstate highway system, the bridge carries an estimated 162,000 vehicles per day.

blandis@projo.com