The demolition of the north half of the Mulholland Bridge over the 405 Freeway is progressing on schedule.
Officials Saturday night said the work that's prompted the total shutdown of the heavily-traveled freeway, dubbed Carmageddon II, should be finished by the completion deadline of 5 a.m. Monday.
Workers, however, hit a snag just after 4 p.m. Saturday when a big chunk of the bridge gave way, collapsing onto a hillside while still attached to a large support column.
The work was temporarily halted for a short time while engineers checked out the fallen section. No one was injured in the collapse and the bridge demolition later resumed.
Dave Sotero, a spokesman for Metro, the agency overseeing the $1 billion widening of the San Diego (405) Freeway, said that it's not clear what caused the large chunk of the bridge to fall.
The chunk fell from the eastern span of the bridge onto the slope leading down to the edge of the freeway.
"During the demolition of a huge bridge like this, it's not unusual for pieces of all sizes to come down," said Dan Kulka, of Kiewit Infrastructure West Co. "Although we didn't anticipate this large of a piece to come down, this is certainly not unusual."
"As soon as it happened we stopped and … had our structural engineers analyze it and redevelop the plan. And now we will continue to demolish it," he said.
Around 6:30 p.m., another large section of the bridge came crashing down on the west end.
A 10-mile section of the 405 is closed between the 10 and 101 freeways.
Other than having to chase some motorists, skateboarders, and walkers off the closed stretch, officials reported few problems in the early hours of "Carmageddon II."
Areas that saw heavy traffic Saturday included the northbound lanes of the 405 Freeway south of the closure area, the 10 Freeway and some Westside surface streets, including Pacific Coast Highway.
The Hollywood and Harbor freeways near downtown saw their usual slow-and-go traffic.
Canyon roads such as Malibu and Topanga saw heavier-than-normal traffic. And truckers were reportedly using Sepulveda Boulevard to detour around the freeway closure, prompting police motorcycle officers and moveable signs to be utilized to head the truckers off at the pass.
Traffic in the San Fernando Valley was mostly light. Canyon roads linking the Valley to Beverly Hills and Hollywood also flowed.
The California Highway Patrol said they spotted skateboarders on the 405 at Santa Monica Boulevard but they disappeared before police could talk to them. Officials also reported a wrong-way driver entering an off-ramp at Valley Vista Boulevard.
Anyone caught trespassing faces anything from a verbal warning to an arrest. Officials hope that they don't see a repeat of a stunt last year, in which a trio was photographed having a candle-lit dinner in the middle of the closed freeway.
The closure of the nation's busiest freeway section officially began late Friday night at midnight, halting traffic on a 10-mile stretch until Monday morning.
Officials closed the highway to demolish the north half of the Mulholland Drive overpass as part of a $1 billion freeway widening project between the Westside and the Valley.
The south side of the overpass was demolished during last year's original Carmageddon.
A new southern side has already been built and will carry all Muholland traffic while a new northern section is constructed.
Days before the latest freeway closure, officials began blitzing the airwaves to urge residents to stay away from the 405, hoping to avoid gridlock.
"With public cooperation, this will be a non-event,'' County Supervisor Zev Yaroslavsky has said. "Let's turn 'Carmageddon' into 'Carma-Heaven' or 'Schmarmageddon' or any other 'geddon' you want to dream up.''
Extra traffic officers were deployed along the route to look out for problems and direct traffic. The L.A. Fire Department deployed a squad of firefighters on motorcycles to respond to emergencies quicker in the hillside areas of the Sepulveda Pass.
Caltrans began using 30 electronic signs along L.A. freeways to warn of the closure and to post alternate routes. The agency is also monitoring traffic cameras.
City News Service contributed to this report.