PORTSMOUTH — Deterioration in the concrete beams of the Cove Bridge on Hummocks Point Road has prompted the state Department of Transportation to put a 10-ton limit on the weight of vehicles using that span in and out of the Island Park neighborhood.

The ban prompted the School Department’s bus contractor to reassign about a half dozen children to school buses that do not use the bridge, according to a school spokeswoman.

The DOT order will add a little more time to bus runs but will not affect the cost of the contract between the School Department and its contractor, First Student, the spokeswoman said. School buses weigh 15 tons, 5 tons over the limit.

Town Administrator Robert G. Driscoll said the weight limit will pose an inconvenience to commercial vehicles headed to and from Island Park. DOT recommends school buses and trucks use exit 2 off Route 24 to Boyd’s Lane as an alternate route to Island Park.

Cove Bridge was built in 1961, in the aftermath of Hurricane Carol, as an “escape bridge” that gave Island Park residents a second way out of their tidal neighborhood in case of emergency, Driscoll said.

DOT spokesman Bob Smith could not say yesterday when the bridge might be repaired or replaced.