The state Department of Transportation (DOT) is completing its design for the rehabilitation of the Glen Road bridge, which crosses above the Lake Zoar section of the Housatonic River, linking Sandy Hook to River Road in Southbury.

DOT spokesman Kevin Nursick said this week he expects that DOT will advertise the project for construction bids in mid-June.

It is expected that the bridge rehabilitation project would begin in April 2014, he said.

“Construction will occur during alternating one-way traffic [on the bridge], with possible short-term [bridge] closures, as required, for structural repairs, “ he said.

Short-term bridge closures would include the use of detours on adjacent roads and on Interstate 84, he said.

DOT has estimated that the Glen Road bridge repairs would cost approximately $6 million.

The bridge, which carries the unmarked State Route 816 across the river, is listed as structurally deficient, resulting in the span receiving a “poor” rating from the DOT, requiring that it be rehabilitated.

The bridge locally is known as the Silver Bridge, stemming from its previous silvery paint color. The bridge is now painted brown.

The span was constructed in 1936. The DOT performed a major improvement project on the bridge in 1986. The two-lane, 308-foot-long truss-style bridge has extensive patches of surface rust apparent across its steel members.

The bridge is listed on the Connecticut Historic Bridge Inventory and is eligible for placement on the National Register of Historic Places. The span carries about 3,100 vehicles daily.

It is expected that the bridge project will take one-and-a-half construction seasons to complete. Construction seasons typically extend from April 1 to November 30.

During the first planned construction season, extending from April through November 2014, the bridge would be closed to traffic to allow structural repairs to be made. During that period, traffic that otherwise would cross the Glen Road bridge would be detoured to the Rochambeau Bridge on Interstate 84.

Remaining work on the bridge, including its cleaning and painting, would occur during the first half of the following construction season, from April through July 2015. During that four-month period, alternating one-way traffic would be allowed on the Glen Road bridge.

The physical deterioration of the Glen Road bridge will be corrected to prevent the span from posing travel safety issues for the public, according to DOT. The work will include steps to eliminate ponding that occurs on the bridge in wet weather.

The federal government would cover 80 percent of bridge project costs, with the state covering the remaining 20 percent.

In June 2011, DOT held an informational session in Newtown to explain the bridge improvement project.