Levine Leichtman Capital Partners (LLCP), a Los Angeles-based private equity firm, announced today that it has completed the sale of short-line operator Regional Rail LLC to 3i Group plc.Based in Kennett Square, Pennsylvania, Regional Rail operates short lines and rail-related businesses in the U.S. Mid-Atlantic region with more than 155 miles of track. The company was formed in 2007.The company serves customers in the agriculture, lumber, energy and metal products sectors. Its subsidiary, Diamondback Signal, provides engineering, construction and maintenance for grade crossings throughout the nation.