The 405 Freeway will be completely shut down from the 10 to the 101 freeways for 53 hours. The closure will begin Friday night, July 15, and last through Monday morning, July 18.
Carmageddon is part of a $1 billion freeway improvement project that will lead to a new Mulholland Drive Bridge.
Drivers use the Sepulveda Pass for 250,000 trips on a single weekend day for work, shopping, access to the airport and the beach.
Metro is promising to add 61 buses to eight key bus lines that weekend to ease the traffic nightmare.
"We're going to be offering free rides between the San Fernando Valley and the Los Angeles area via the Orange Line and the Red and Purple lines, so it's going to be very easy for people to use transit," said Metro spokesman Dave Sotero.
Metro fielded questions from noon to 1 p.m. People were allowed to email questions in advance of the chat.
Several commuters posed questions involving getting to and from Los Angeles International Airport. Metro urges travelers with an international flight to book a hotel room near the airport the night before their flight.
Other questions related to specific closure times, emergency services and suggested alternates.
In addition to using the Internet to get the word out, the MTA is also taking to the airwaves to put out their warnings. Wednesday morning, "CHiPs" actor Erik Estrada was shooting public service announcements along the shoulder of the 405 Freeway in both Spanish and English.
"Please, either stay home, chill out, or avoid the area if you can. Plan ahead," Estrada said, giving the camera a thumbs-up and a wink.
The Los Angeles Police Department is asking more than 100 celebrities to tweet words of warning to their fans.
"Hopefully Lady Gaga, Ashton Kutcher, some of our more versed and popular Twitter accounts will get that message out for us," LAPD Lt. Andy Nieman said.
Officials said the main message to people is to plan ahead, avoid the area or stay home that weekend.
Metrolink is also beefing up services. It will operate its Ventura County line, which typically doesn't offer weekend service.
Beat Carmageddon with ABC7
The 405 shuts down the weekend of July 16-17, and ABC7 Eyewitness News is your home for the latest traffic news and information. Follow @abc7 and @BeatCarmageddon on Twitter, and use the hash tag #abc7traffic.
ABC7 has also partnered with Waze to help navigate the traffic. Download the Waze app, which provides free turn-by-turn GPS navigation based on the live conditions of the road. Join the community of drivers in Southern California today and beat Carmageddon.