** FILE ** A single line of traffic, right, moves along the elevated Central Artery toward the Leanord P. Zakim Bunker Hill Bridge, background right, Saturday, March 29, 2003, in Boston. After more than a decade of construction and $14 billion spent to replace the old highway with a tunnel under the city, the effort has dramatically changed the face of the downtown/waterfront area of Boston. (AP Photo/Michael Dwyer, File)