The Arlington County Board approved two major infrastructure projects Saturday, authorizing $13.7 million worth of work to replace aging utilities across the county.

The upgrades include an $8 million contract to replace 10 miles of copper cable with fiber optic cables to connect 101 traffic signals along the Rossyln, Crystal City and Columbia Pike corridors, and allow future expansion of the county’s traffic communications systems.

The board also awarded a $5.7 million contract to put utilities underground along Columbia Pike from South Wakefield Street to Four Mile Run Drive. This second phase of the project also will resurface the street, build wider sidewalks and add new street lighting, bus shelters and street trees.

The second contract, awarded to Sagres Construction Co., is part of the county’s initiative to improve Columbia Pike where new water, sanitary sewer and gas utility lines have already been installed. The project is paid for with federal funds, state revenue-sharing and County-matching funds. Construction on the new phase will begin in July and run through fall 2013.

The fiber optic project, awarded to Chesapeake Electrical Systems Inc., is also a second-phase project which was initially passed in January 2011. In addition to improving traffic lights, it will give emergency vehicles faster and safer access through intersections, and allow real-time notification of problems to motorists. This second of three phases should be completed by next May, county officials said.

The board also heard, but did not act upon, County Manager Barbara Donnellan’s recommendation for a capital improvement plan which will cost $2.45 billion over the next 10 years. A series of workshops are planned before the board vote in late July.