Carmageddon could result in 20-mile back-up on 405 [Video]

"Carmageddon" traffic could back up 20 miles on the 405 Freeway -- as far south as the 110 Freeway -- under a worst-case scenario, transportation officials said.

During a live chat on the Times website, Mike Barbour, Metro's director for the I-405 Sepulveda Pass widening project, said traffic "could get bad on the south side."

Carmageddon: Full coverage of the 405 Freeway closure

"The worst case is it could be backing up to the 110," Barbour said. "We’re talking a significant 20 miles or so. it really depends on if people are staying away or not."

Mayor Antonio Villaraigosa reiterated the call to stay off the freeways during the planned shutdown of the 405 Freeway between the 10 and the 101 freeways. He urged people to eat and shop locally and said he expects the weekend events to turn into "Carmageddon hype" -- but only if people follow instructions.

Offramps and onramps will begin closing at 7 p.m. Friday, with a full freeway closure at midnight. The freeway is scheduled to reopen by 5 a.m. Monday, but transportation officials said they have built in extra time and may be able to open the freeway earlier.

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-- Kimi Yoshino