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.

Though schedules aren't final, CTA expects to begin with track work, followed by station renovations, power upgrades and signal improvements. Seven stations will undergo extensive renovations, and six will receive repairs. Track and track-signal improvements are expected to eliminate slow zones and improve travel speeds.

"We're still in the early phases of design, so several details have yet to be finalized," says CTA spokeswoman Catherine Hosinski. Once completed, CTA anticipates renovations will shave 10 minutes off the 45 minutes currently required to travel between downtown and O'Hare. Signal and electrical upgrades will allow CTA to increase capacity, while new "turnback tracks" will accommodate shorter runs during peak travel hours.

At a press conference, Chicago Mayor Rahm Emanuel (D) indicated the program, like others CTA has undertaken in recent years, is critical to "modernizing our transit system for the 21st century." Among other improvements, plans include upgrades of wireless infrastructure to provide more reliable voice, data and web service in subway tunnels. The Blue Line, which services 80,000 commuters daily, will remain operational during construction.

Emanuel indicated the overhaul is the most comprehensive since the line was extended to O'Hare, in 1983. Work will be funded by local, state and federal sources.