PROVIDENCE — The state Department of Transportation said yesterday that it is closing three bridges, one in Cumberland and a pair in Hopkinton, because of deterioration discovered in inspections. The DOT also said it will install a barrier to divert traffic away from a weakened section of a Providence bridge.

The bridges are:

•The Arnold Mills Bridge in Cumberland, a timber bridge that carries Sneech Pond Road over Abbott Run, a stream leading from the nearby Pawtucket and Arnold Mills reservoirs. Built in 1886 and reconstructed in 1985, it has been posted for a maximum of three tons and was to be closed today. The DOT said it has no timetable for its replacement.

•Two more timber bridges, one after the other in Wyoming, which carry Bridge Street over the Wood River on the Hopkinton-Richmond line. The northern one was found to be deteriorated, but both will be closed immediately. The DOT said it was closing both because they are so close together. The bridges were built in 1932 and rehabilitated in 1960.

•The Randall Street Bridge, which carries Randall Street over the Moshassuck River in Providence, will get barriers placed today. A recent inspection found the northernmost beams deteriorated, and the agency said it will place barriers to shift traffic away from them.

The DOT said it was already planning to replace all four bridges, starting with the Wyoming bridges this year using $2.3 million from the American Recovery and Reinvestment Act, the national economic stimulus program. The DOT said it expects work to begin in the middle of this year and take approximately two years to complete. Motorists will be directed to use a detour of about 1 mile, using Main Street and Bank Street.

DOT Director Michael P. Lewis said the department regrets the inconvenience the closings and restrictions may cause, but he said that the DOT’s top priority is safety. “We must institute these changes until repairs can be made,” he said.

blandis@projo.com