Everyone will find out soon enough as authorities prepare to close Interstate 405 for 53 hours beginning Friday night. Around the afternoon rush hour, the city will activate its emergency operation center before highway officers begin blocking access to on- and off-ramps. Then they'll close freeway lanes one by one until they reach a full shutdown by midnight.
Non-emergency street maintenance and repair projects will come to a halt. Police, firefighters, paramedics and traffic engineers will be on standby to respond to any crisis that may arise.
For weeks, officials have issued grim warnings about the closure in the same tones reserved for floods and threatening wildfires.
To prepare the public for the closure, they flashed signs on freeways as far away as San Francisco reminding drivers over and over: Stay off the 405 July 16-17. They recruited celebrities with large followings on Twitter, such as Ashton Kutcher and Kim Kardashian, to get the message out.
Facebook agreed to direct some 6.6 million driving-age people in the greater Los Angeles area to the Metropolitan Transportation Authority's Facebook page detailing the latest traffic conditions this weekend.
Transportation experts said the publicity campaign seems to be working.
They now predict that while there will likely be some backups on other freeways and on surface streets near the 405, the weekend shouldn't end in massive gridlock.
"It's going to be fine, people had a lot of warning," said Lisa Schweitzer, a professor of urban planning at the University of Southern California.
Experts compared the shutdown to other big planned events, such as the 1984 summer Olympics, Los Angeles Lakers championship parades and Michael Jackson's memorial service two years ago.
The disastrous traffic jams predicted for each of those events never materialized. People knew to stay off the road. In fact, city residents marveled that, during the two weeks of the Olympics, traffic was actually much lighter than usual.
"For the 1984 Olympics, by repeating how complex and difficult it's going to be, some people chose not to travel, to take public transit or go away for vacation," said Martin Wachs of the Rand Corp. think tank.
That could be the case again this weekend. Not that some people aren't still worried, as closing that section of the 405 for such a long time is pretty much unprecedented.
Judy Feldman of New York and her husband had planned a trip to Southern California long before they learned of the closure. They planned to spend the weekend going into the city.
Now, all she's been hearing has been one message about their plans: "No, I wouldn't do that."
Their planned trip to the popular Getty Center museum is out, as it's located right in the middle of Carmageddon and will simply close down that weekend. So will the nearby Skirball Cultural Center.
"We'll be glad when Monday is here," said Skirball spokeswoman Mia Carino, who is cautiously optimistic that she'll be able to drive to work that day.
Feldman and her husband still hope to get to Los Angeles to take in other museums.
Transportation officials say the closure is necessary to replace the 50-year-old Mulholland Bridge as part of a $1 billion project to widen a perpetually bottlenecked segment of the 405.
That stretch goes through the Sepulveda Pass, which connects the San Fernando Valley to Los Angeles' West Side.
They say a full closure is necessary to demolish one side of the span, and they picked this weekend to minimize impact to traffic on a workday. They expect another closure next year to replace the other half.
On a typical July weekend, about a half-million vehicles use that section to get to such major destinations as Los Angeles International Airport, UCLA, Beverly Hills and numerous popular beaches.
To discourage driving, the city is offering free rides on the subway and certain bus lines and adding more commuter train service. Hotels and restaurants are offering discounts.
Around town, some people are organizing neighborhood walks, bicycle rides and even "Carmageddon" parties.
Joann Killeen, who lives near the 405, is going to attend such a party Saturday at her next-door-neighbor's house.
"We're going in our garages and looking for old Scrabble boards and Monopoly games and we're going to bring potlucks and just be silly from about 5 o'clock until midnight," she said.