Trouble down the road in L.A.?

LOS ANGELES – The alarms have been sounded and the preparations have been made.

Now, only two questions remain: Will “Carmageddon,” the shutdown of a 10-mile stretch of one of the busiest highways in the United States, on one of the city’s busy summer weekends, bring the City of the Angels to its knees?

Or will this too come to pass, just like so many other predictions of the apocalypse? (Remember the Oakland radio preacher who just last spring put up billboards promising the world would end on May 21.)

“Like Y2K,” Ashley Nazarian said dismissively, referring to the much-hyped worldwide computer data meltdown that never happened as the clock turned to Jan. 1, 2000.

Nazarian, property manager for the Sherman Oaks Galleria, a mall that is located next to an exit on the affected stretch of the 405, might be worried but she isn’t.

Word that part of the freeway will be shut down for repairs for 53 hours beginning at midnight tonight has been spread so far and wide by now that she believes people will stay away.

Still, the UCLA Health System, which runs the huge Santa Monica-UCLA Medical Center, is taking no chances. It has three helicopter companies on standby to transport patients and human organs in the event of emergency operations. It is laying in extra medical supplies and 5,200 boxed lunches for its staff.

Authorities, meanwhile, have been preparing the public for the closure for weeks. Signs on freeways as far away as San Francisco have been flashing the same message over and over: Stay off the 405 July 16-17. On Thursday, Facebook said it will direct about 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.

Numerous celebrities, including Tom Hanks, Piers Morgan and Maroon Five’s Adam Levine have joined the cause, taking to Twitter to get the message out.

William Shatner, who as Capt. Kirk of “Star Trek” traveled in space where no man had gone before, indicated that he won’t be going anywhere near the 405.

“LA friends, the 405 closes this weekend in what surely will be Carmageddon,” Shatner tweeted.

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.

Transportation officials say the weekend 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.