The city of Chicago is launching a $492-million, four-year program to overhaul a mass-transit line that extends between downtown and O'Hare International Airport.

Beginning in 2014, the Chicago Transit Authority's (CTA) Blue Line will undergo extensive track improvements, in addition to signal, power and station-house upgrades. Rather than complete track replacement, plans call for renovations along the 12.5-mile line, which includes subway tunnels, elevated structures and ground-level track.