Route 95 will be re-striped in both directions to shift more weight to the bridge’s main support girders.

The Providence Journal / Bob Breidenbach

The 49-year-old highway bridge carrying Route 95 over the Pawtucket River will be off -limits by the end of the month to loaded tractor-trailers and other large trucks, due to deterioration discovered in metal brackets that help support the bridge.

The bridge, in Pawtucket, will have a posted weight limit of 22 tons, which will not affect passenger vehicles, light trucks, buses and ambulances.

Route 95 will be re-striped in both directions to shift more weight to the bridge’s main support girders.

Most large trucks traveling Route 95 can avoid the weight restriction by taking Route 295, which adds about six miles. Local detours are still being worked out.

The bridge, known as number 550, is actually two bridges built side-by-side in 1958 as part of the original interstate highway system. The 700-foot bridges rise 57 feet over the river.

“Bridge 550 is safe for travel,” state Department of Transportation Director Jerome F. Williams said in a statement. “The proactive changes … are being done to ensure that.”

The problem is deterioration to cantilevers that extend the road outside the bridge’s main supporting girders, according to the DOT.

“On the sides of these bridges we have some brackets that are attached to those main girders,” said Kazem Farhoumand, acting DOT chief engineer. “Basically the concept is the same as a bracket you use for a shelf in your house. We have found some deterioration in these.”

To further reduce weight on the brackets and extend the life of the bridge, the re-striping will shift traffic lanes away from the outer edges of the bridge, so that the main support girders can bear more of the load, Farhoumand said. “We’re narrowing the shoulder on the low-speed sides and enlarging it on the high-speed sides.”

The bridge will continue to have three 12-foot traffic lanes in each direction. The shoulder near the high-speed lane will shrink to an average of 4 feet wide; the low-speed shoulder will expand to about 7 feet, according to the DOT.

Re-striping work was due to begin last night on the northbound lane, continuing through 10 this morning, weather permitting.

Southbound re-striping is due to begin tomorrow night at 11 and should finish by 5:30 a.m. Monday, before the morning rush.

At least one lane will be open throughout the re-striping.

The DOT pledged yesterday to cooperate with Pawtucket officials to identify detours for trucks that service the local area. The recommended detours will be publicized before the bridge weight limit is posted, probably in the next two weeks. The state police will enforce the weight limit.

In Pawtucket, the George Street on-ramp to Route 95 north, after Exit 27, will close permanently when the bridge is posted, to allow for repair work, according to the DOT. The ramp will stay closed until the bridge is eventually replaced.

Bridge 550 is on the department’s replacement list, said DOT spokeswoman Dana Alexander Nolfe. The estimated replacement cost is $40 million to $50 million. “We’re looking at a timetable right now,” she said.

The restrictions imposed on the bridge stem indirectly from the collapse last summer of a highway bridge in Minneapolis. That fatal accident brought national attention to bridge safety and inspections. With the collapse in mind, the Rhode Island DOT decided to reinspect about 35 bridges that lack redundant safety measures that would prevent a sudden collapse if a bridge suffered a major problem.

Bridge 550, which had received a scheduled inspection last year, was among those non-redundant bridges reinspected in late summer, said Farhoumand.

“The inspection process has two components,” he said.

“You look at everything, touch everything, tap everything, take pictures. You take that information back and catalog it. And then you have to do some engineering to determine the load-carrying capacity of the bridge, based on its age and condition.

“We have started that for this bridge. We’re about 40-percent complete. Last week it was brought to our attention that there were a few areas of concern with the bridge. So we started looking at it immediately.”

Bridge 550 was built for 60,000 cars per day. The daily volume is now 162,000.

“Bridges are similar to people,” Farhoumand said. “As you hit your 40s and 50s, things start going wrong. This bridge is 50 years old. It has carried a lot of load.”

marsenau@projo.com