LOS ANGELES -- The new Metro Gold Line extension from downtown Los Angeles to the Eastside opened Monday morning for regular service.

Some 50,000 people took advantage of the offer of free rides along the route Sunday.

And on Saturday, a host of area leaders, including Los Angeles County Supervisor Gloria Molina and Mayor Antonio Villaraigosa were on-hand for ceremonies marking the opening of the six-mile rail line that includes 1.7 miles of underground travel.

"For the first time in nearly half a century -- since the last trolley ran down 1st Street -- rail will again carry passengers from downtown L.A. to East Los Angeles," said Villaraigosa. "This caps a 20-year battle to bring rail back to East L.A. -- one of the most transit dependent communities in Los Angeles."

The new leg was officially dedicated as the Edward R. Roybal Metro Gold Line Eastside Extension in honor of the late and longtime politician who represented parts of Los Angeles County in the U.S. House of Representatives for three decades.

"As a member of the U.S. House of Representatives for 30 years, he was a staunch supporter of efforts to bring rail to the Eastside and he worked long and hard towards that end," said his daughter, U.S. Rep. Lucille Roybal-Allard. "It has been my pleasure to continue that fight ... Today his dream of affordable, clean and efficient transportation is becoming a reality."

The extension will expand the Gold Line from Pasadena to the Eastside via downtown. As a treat for the public, all Gold Line rides will be free this Sunday only.

The city first began discussing the extension about 22 years ago. The MTA is expecting close to 13,000 riders each day once service begins.

Many people on the Eastside are dependent on mass transit, and they'll now be able to access the Union Station rail hub and all the destinations it serves.

There were some opponents to the new extension, including some who wanted the line to be 100 percent subterranean.

Others have raised safety concerns, but Metrolink says it has gone through all the safety checks and requirements.

MTA officials were warning pedestrians and motorists to be mindful of the new route, and to use extra care at intersections and heed flashing train signs and guard rails.