Work on the Mulholland Bridge overpass -- part of the massive "Carmageddon II" weekend freeway shutdown -- was temporarily halted Saturday after a big piece of the bridge fell.
Officials on scene said a portion of the overpass had fallen, and work on top of Mulholland was stopped following the incident just after 4 p.m. Saturday.
No one was injured in the incident, and workers expected to meet their completion deadline of 5 a.m. Monday, according to a spokesman for the contractor.
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 added.
Originally, officials said a pillar had fallen.
During an earlier afternoon briefing, officials had said the pillars supporting the bridge weigh up to 1 million pounds each. Four must be demolished as part of the work this weekend.
Until the chunk of bridge fell, things had been going smoothly for the 10-mile closure of the San Diego (405) Freeway, the nation's busiest.
Los Angeles Mayor Antonio Villaraigosa had said Saturday afternoon that work was one hour ahead of schedule.
And other than having to chase some motorists, skateboarders, and walkers off the closed San Diego Freeway, they reported few problems in the early hours of "Carmageddon II."
Areas that saw heavy traffic Saturday included the northbound lanes of the 405 Freeway, the 10 Freeway and some side streets of West Los Angeles, said CHP Officer Juan Galvan.
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.
"We want to make sure that everybody's safe," Galvan said. "There's a lot of construction workers out there and there's a lot of machinery out there."
Anyone caught trespassing faces anything from a verbal warning to an arrest, Galvan said. 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 Friday, halting traffic on a 10-mile stretch until Monday morning.
Officials closed the highway to demolish the Mulholland Drive overpass as part of a $1 billion freeway widening project between the Westside and the Valley.
Days before the closure officials began blitzing the airwaves to urge residents to stay away from the freeway, 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.
On Saturday, construction crews used a hoe ram -- a hydraulic punch on the end of highly maneuverable boom -- to demolish the northern half of the Mulholland overpass, which was sliced in half lengthwise during the first "Carmageddon" on July 16-17, 2011.
City News Service contributed to this report.