Officials caution drivers on Carmageddon II

First, they will dump 1,200 cubic yards of dirt under the Mulholland Drive bridge, enough to create a cushion 4 feet thick.

Then a small army of construction workers and equipment will swarm the 405 Freeway below, and over the next two days knock down and haul away more than 300 tons of reinforced steel from the bridge’s northern side.

Welcome to Carmageddon II, a major hurdle in a $1-billion road improvement project that includes demolishing the second half of the 80-foot-tall bridge so it can be rebuilt wider, and adding a northbound 405 carpool lane through that stretch of the Sepulveda Pass.

FULL COVERAGE: Carmageddon II

It all starts after rush hour Friday night, when the California Highway Patrol shuts down a 10-mile stretch of the nation’s busiest freeway for the second time in 14 months, crossing fingers that hundreds of thousands of motorists will stay home this weekend or at least avoid creating mayhem trolling surrounding streets and freeways.

The first closure — which earned the popular moniker Carmageddon — was held over a weekend in July 2011, when construction crews took down the south side of the bridge in a highly choreographed operation.

And the traffic jams that officials repeatedly warned about during an aggressive public relations campaign — Lady Gaga and other celebrities were enlisted to send Twitter messages to dissuade people from driving — failed to materialize even though a half-million motorists pass through the closure zone, between the 10 and 101 Freeways, on an average weekend.

Instead, traffic over that weekend was eerily calm, the closure ended 17 hours early and Mayor Antonio Villaraigosa and other officials proclaimed Carmageddon had turned into “Carmaheaven.”

“The reason Carmageddon was so successful last summer is that we had the cooperation of the general public in staying home and out of their cars.... It turned into one of the most peaceful and pleasant weekends in recent memory,” county Supervisor Zev Yaroslavsky said.

“If we have the public’s cooperation again, this weekend should be a repeat of last summer. However, if motorists are complacent and revert to normal car usage, we could easily have the traffic nightmare we have all been trying to avoid,” he said.

Caltrans District 7 Director Mike Miles quantified the necessary cooperation, saying that two-thirds of those drivers who normally use that stretch of the 405 Freeway need to stay off the road for the weekend to be a success. A worst-case scenario, Miles said, would have traffic backed up to Kern County in the Central Valley.

“The risk factors that made us all to be extremely careful last time around.... Nothing has changed,” said K.N. Murthy of the Los Angeles County Metropolitan Transportation Authority. “All it takes is one incident... The elasticity in the existing freeway system is very minimal; it can only take so much additional traffic.”

Metro spokesman Dave Sotero added: “If you are making a discretionary trip, please do not. Go back in the house.”

Crews will begin shutting down freeway ramps along the closure area as early as 7 p.m. Friday. They will block some lanes of traffic about 10 p.m. and expect to have all of the lanes on that part of the 405 Freeway closed by midnight. The plan is to reopen the freeway early Monday, before the morning rush hour. And unlike last year, officials don’t see much chance of an early reopening, saying that they plan to use the opportunity to perform other work.

Officials are offering drivers several tips and transit options to get through the weekend. Among them:

Caltrans suggests that drivers who must use the freeway system first look at their new traffic website, QuickMap. Those using public transit can check out Metro’s Trip Planner.

Motorists can call 511 or click on “go511.com to get real-time traffic information. They can also monitor real-time traffic reports on radio, television or the Internet.

People who find themselves in need of non-emergency assistance while on the freeway can call #399 to summon the Freeway Service Patrol.

Metrolink has added seven round trips on its commuter rail service between Los Angeles and Chatsworth.

Major global navigation companies, such as Garmin, have been notified of the closure in hopes that they will reroute drivers away from the area.

Metro officials say that before drivers hit any road — especially a freeway — they should plan two or three alternative routes, the further east from the closure area the better.

Officials say that those who do get on the freeway should have plenty of water, vital medications and a working radio in case they hit a bad traffic jam. A full tank of gasoline would be a good idea too.

The CHP also vows to arrest anyone who goes on the freeway illegally, like those people who photographed a table set for dinner on empty freeway lanes during the first Carmageddon.

It’s unclear if motorists are taking the second closure warnings as seriously as the first. Some, like musician Judson McKinney, don’t believe the hype.

“It was kind of like the Y2K thing,” McKinney said of the first Carmageddon while cleaning the inside of his van at a do-it-yourself carwash in Echo Park. McKinney said he would probably drive during this weekend’s closure even though he can’t predict what “this one’s going to be like.”

“L.A.’s bad enough anyway,” he reasoned.

Other drivers said they plan to ditch their cars for the weekend or stay away from the closure area.

Eating lunch at Philippe the Original on Alameda Street in Chinatown, 60-year-old Maryann Davern said she drove to downtown from her home in Redondo Beach during the week to run an errand because she didn’t want to compete with any weekend traffic.

“I didn’t want to fight this on the weekend,” Davern said. “I think this time everyone’s expecting it not to be a problem, but expect the unexpected, I guess.”

ari.bloomekatz@latimes.com