BRUNSWICK — Two bridges between Brunswick and Topsham will be periodically closed for repairs in coming weeks.

The Merrymeeting Bay bridge, which carries Route 196 across the Androscoggin River, is undergoing surface repairs starting in May, the Maine Department of Transportation said. All four lanes of the bridge will be open during the day, but at night traffic may be restricted to one lane in each direction.

The ramp from Route 1 northbound to Route 196 westbound will be closed for approximately one month beginning in early May. Drivers can detour across the Route 24 or green bridge in downtown Brunswick.

Work on the ramp from Route 196 eastbound to Route 1 northbound will also begin in early May and will take place in two phases. The ramp will be closed six weekend nights; traffic will be diverted to the Route 24 bridge. During the day the ramp will be narrowed to one lane.

Further west on the Androscoggin, the Black Bridge is also closed.

After a driver struck a support beam on the one-lane bridge in early April, the DOT closed the bridge and engineers discovered the pressure-treated wooden guard rails were rotting.

“The amount of interior rot was surprising,” DOT spokesman Mark Latti said. “It was decided then that a more thorough inspection of the bridge needed to be completed on the guardrails and the decking.”

In order to do that inspection, the DOT needs an under-bridge crane that rides on train tracks. Only three such cranes exist in the country, and the earliest the DOT can secure one is in July.

Until the DOT determines the extent of the rot, the bridge will be closed.

Latti said given how unique the Black Bridge is, it would be difficult to bring it up to modern engineering standards without totally replacing it, which he said was unlikely to happen given the proximity to the Route 24 bridge.

“The fact that it’s suspended by those steel rods, the fact that it’s underneath a railroad bridge, (has) alternating one-way traffic … in some ways there’s nothing you can do to that bridge in order to bring it into compliance with modern engineering standards,” he said.

When asked if the bridge would become one-way if it opens again, an idea that was raised by Brunswick Town Councilor David Watson at a recent council meeting, Latti said it is too soon to tell.

“Until that thorough inspection is completed, it’s really too early to discuss traffic patterns,” he said.

Emily Guerin can be reached at 781-3661 ext. 123 or eguerin@theforecaster.net. Follow her on Twitter: @guerinemily.

The Black Bridge between Brunswick and Topsham is closed indefinitely for repairs.