FALMOUTH — Maine Department of Transportation engineers will close one lane of traffic on the Route 26/100 bridge across the Presumpscot River at 8 a.m. on Thursday and use an under-bridge crane to perform a structural inspection.

Motorists will be limited to one lane of alternating traffic until later in the day.

The inspection is part of DOT’s plan to dismantle the current bridge and build a new bridge downstream. The new bridge will shift the traffic pattern slightly, but DOT officials say it will be constructed as close as possible to the old one.

The project, which is projected to cost $10.5 million, is scheduled to be completed in June  2012. The replacement bridge is scheduled to open for traffic in October 2011.

“The bridge will remain open the entire time,” DOT Project Manager Nate Benoit said. “We want to limit the impact to the community.”

The new bridge will replace a bridge constructed in 1932. Benoit said the current steel connections are beginning to deteriorate at an accelerated rate, which is why DOT decided to replace, rather than repair, the bridge.

“It has lived out its life, but it’s still safe,” he said.

The bridge, also called the Railroad Crossing Bridge because it crosses the Pan Am railroad line, is a popular thoroughfare and commuter route for those traveling between West Falmouth and Portland, and is also utilized by the METRO bus service.

Emily Parkhurst can be reached at 781-3661 ext. 125 or eparkhurst@theforecaster.net