The U.S. Army Corps of Engineers is set to perform "critical maintenance" on the Bourne Bridge in Cape Cod, requiring two of its four vehicle lanes to close until May 20. The work will include pavement resurfacing, repairs to steel joints damaged by snow plowing, and maintenance of roadway lights and drains. The closure will be in effect 24 hours a day during the three-week period. The state Department of Transportation has begun the process of identifying contractors to replace the nearby Sagamore Bridge, which is expected to take at least a decade and cost $4.5 billion.