The decision to brace and repair the stricken portion of the Santa Monica Freeway in lieu of a more costly, months-long effort to tear down and replace it, was based on engineering tests showing the structural integrity of the freeway deck remained stronger than anticipated.
The project was expected to commence immediately and continue around the clock until completed, California Governor Gavin Newsom said.
The announcement came during a morning press conference by the governor, Mayor Karen Bass and other officials at the scene of Saturday's fire, which investigators on Monday determined was the result of arson.
More than 100 columns of reinforced concrete supporting the elevated freeway and the surface of the roadway itself were badly scorched in the blaze, forcing closure of a stretch of the east-west artery in both directions.
The Santa Monica Freeway, also known as the Interstate 10 - or "the 10," in local parlance - is traversed by some 300,000 vehicles daily, with the downtown L.A. portion often congested under normal circumstances.
With the damaged section shut down, officials have urged commuters to avoid downtown and to take public transit instead when possible, or to work from home.
Still, detours around the closure were expected to ripple out and compound heavy traffic across California's largest city, marking one of the area's worst transportation disruptions since the Northridge earthquake flattened two parts of the same freeway in 1994.
Newsom said he expected that the latest repair project to take closer to three weeks than five, with contractors being offered bonus incentives for completing the work ahead of schedule.
Meanwhile, arson investigators were continuing their work seeking to identify the person or persons responsible for setting the fire, Newsom said.
State Fire Marshal Daniel Berlant said on Monday authorities had determined the fire's origin, but he gave no details about how investigators reached their conclusion or about the precise way in which the blaze was ignited or why.
The flames erupted in the early morning hours of Saturday and spread through storage yards beneath the freeway filled with stacks of wooden pallets, containers and parked vehicles, authorities said.
Newsom said the state had leased the site to Apex Development Inc, a company based in Calabasas, north of Los Angeles. According to the governor, the state recently sued to evict the company, which he said had quit paying rent and was violating other terms of the lease. Apex did not respond to Reuters' requests for comment as of Tuesday.
(By Steve Gorman; Editing by Alistair Bell)
By Steve Gorman