BIG DIG The Central Artery/Tunnel project will change the way Boston works, but it cost $14.6-billion. (Photo courtesy of bigdig.com) The Commonwealth of Massachusetts and the Massachusetts Turnpike Authority filed suit March 16 against the joint venture of Bechtel/Parsons Brinckerhoff seeking damages of up to $146 million in connection with its role as project consultant on Boston’s $14.6-billion Central Artery/Tunnel project. At particular issue is the escalation in project costs, which went from $2.6 billion in 1982 to the final tally of $14.6 billion. B/PB claims that the charges are without merit. Filed in Suffolk County Superior Court, the civil