$270 million in federal loans will fund one of the state’s largest-ever transportation contracts. The type of project is what one state lawmaker calls the future of transportation building in Georgia. By adding toll lanes, the Northwest Corridor project could relieve congestion on a 30-mile stretch of Interstates 75 and 575 north of Atlanta. It’s a public-private partnership that could cost up to $1 billion. The public’s share would be about a third of that amount.