Officials broke ground Monday on the city's newest light-rail line. The first segment of Sacramento Regional Transit District's "green line" will run just more than a mile, from downtown north to the River District. Eventually, the line will carry public transit riders to Sacramento International Airport. "It's the first great step to a complete transportation system. This is going to connect everything together," said U.S. Rep. Doris Matsui, standing at the future site of the line's initial terminus, 7th Street and Richards Boulevard. "We have an investment in an expanded airport. We're going to have to have another way to get there — and that's going to be light rail." The line will s