SEAL BEACH, Calif.>> In what’s become a rite of summer in Southern California, construction will force the weekend closure of one of the nation’s busiest stretch of highway, threatening to create massive tangles of traffic.

Or will it?

Traffic was smooth after authorities shut Interstate 405 near its junction with State Route 22 and Interstate 605  until 5 p.m. today as crews work to tear down an old connector bridge.for construction Saturday evening.

However the big traffic test comes during the day today.

The demolition is part of a $277 million project to link carpool lanes between the freeways.

The 20 hour-long closure is the latest freeway shutdown in Southern California to stir fears of epic traffic jams, but those worries have so far not come to fruition.

The closure of a section of I-405 in Los Angeles in 2011, followed by a similar shutdown there last year, did not result in “Carmageddon.” Motorists heeded months of warning to stay off the road and the weekend traffic was unusually light.

Transportation officials are hoping for a repeat by warning residents to not only steer clear of the freeways, but also avoid the detours.

They spent nearly a year to prepare for the shutdown. To get the word out, they distributed tens of thousands of fliers, illuminated freeway signs around the region with warnings and dubbed the closure the “Bridge Bash.”

The local newspaper had a naming contest and the winner was the “Orange Jam.”

Officials say the potential for serious backups is real: 300,000 vehicles pass through the stretch of freeway that will be disrupted by the bridge demolition on a typical weekend day.

The best detours available will send drivers on long side-street tours of cities such as Los Alamitos and Seal Beach.