LOS ANGELES (CBSLA.com) — The county’s oldest light-rail line will undergo a $1.2 billion facelift, Metro officials said Wednesday.

Some work has already begun on the Metro Blue Line, which connects downtown Los Angeles and Long Beach, but most of the work will be completed over the next six years, Metro officials said.

READ MORE: 2 People Killed, 3 Critically Hurt In Violent South LA Collision

Metro officials say they will spend $739 million to purchase 78 rail cars and another $130 million to repair and upgrade 52 cars already in service.

“The Blue Line is an old train that’s long overdue for an upgrade,” Mayor Eric Garcetti said. “This investment will make life better for the 90,000 people who ride the Blue Line every day with a safer, more convenient and more comfortable commute.”

Another $82 million will be spent to replace 20 power substations, 19 of which have already been completed. Another $13 million will be used to upgrade overhead power lines in downtown Los Angeles and Long Beach.

READ MORE: Man Shot While Walking Dogs In Hollywood, 2 French Bulldogs Stolen

Rail tracks in Long Beach that have been damaged by moist sea air will also be replaced at a price of $13 million.

Metro officials said some service disruptions will occur during the project. Most of the work is planned for weekends, overnights or during off-peak hours. The Blue Line, which began operating in July 1990, has about 90,000 boardings per day.

“The Blue Line is the backbone of transportation for the central part of Los Angeles County and this investment means that working families can continue to count on this system for decades to come,” Los Angeles County Supervisor Don Knabe said.

MORE NEWS: At Least 2 Homes Destroyed When Wind-Whipped Fire Rips Through Bloomington Neighborhood

(©2014 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services contributed to this report.)