184-Mile Stretch of I-5 Shut Down : Storm: Temporary bridge over road is expected to be up within a month. Caltrans says plans for a short detour may be dropped because local roads might not hold up.

A 184-mile segment of Interstate 5, the most commercially vital highway in California, was put out of commission by the weekend storms, and Caltrans said Sunday that it could take as long as a month to erect a temporary bridge and reopen the road to traffic.

Officials said they will introduce a new type of bridge--using railroad flatcars--while permanent spans are built to replace the twin bridges near Coalinga that collapsed under the pressure of raging storm waters Friday night. In the meantime, traffic has been detoured onto California 99 through Bakersfield and Fresno.

As the clouds and rain receded Sunday and President Clinton declared 39 California counties disaster areas, a California Department of Transportation spokesman indicated that plans for a much shorter detour might be dropped because local roads, waterlogged from flooding, might be unable to stand the stress from the heavy trucks trundling goods up and down the Central Valley every day.

The California 99 detour is expected to cause major truck and automobile congestion as well as considerable delays and economic loss. An extended shutdown of such a long portion of I-5, which carries about 25,000 vehicles a day, could inflict serious financial damage on the gas stations, motels and restaurants that have grown up in the last quarter century to service travelers.

The recent storms created havoc up and down the state, claiming several lives, forcing thousands to flee their homes and flooding vast tracts of farmland. Gov. Pete Wilson said California had sustained several hundred million dollars in damage just since the last round of floods in January, while farm officials estimated that losses from the lastest storms among strawberry and other crops could exceed the $27 million reported from the January floods.

The most spectacular single event, however, was the closure of I-5, opened as a shortcut through sparsely populated farmland between Los Angeles and San Francisco in 1972. The bridges collapsed when floodwaters undermined their foundations, and seven people presumably perished when their cars plunged into the muddy water below.

Caltrans spokesman Jim Drago said that when the flatcar bridge, first envisioned after the Northridge earthquake, is operating, it will carry one lane of traffic in each direction. The collapsed bridges had two lanes in each direction.

“We’ve completely tested this new concept and we have had the prototype in storage at our maintenance station at Lost Hills for several months,” Drago said. “It’s ready to go.”

The Caltrans spokesman paid tribute to engineer Bill Wattenburg, a consultant in nuclear physics at the Lawrence Livermore National Laboratory and a San Francisco radio talk show host, for developing the flatcar concept after viewing damage on the Santa Monica Freeway after the 1994 earthquake.

Whole flatcars fastened together will form the roadway for the bridge, and flatcars sliced in half length-wise will form the girders holding it up.

Wattenburg, interviewed from his Bay Area home, said the temporary bridge will be able to carry twice the weight of most freeway bridges. Were it not for the necessity of preparing the site, he said, it could be installed in as little as two days.

Drago said that when work does begin on reopening I-5, it will probably be in 12-hour shifts, not the round-the-clock work that marked freeway repair in Southern California after the Northridge quake.

“By Monday or Tuesday, we’ll have a much better handle on how we will be able to get in there and get the work done,” Drago added, saying it was possible it could be done even faster than the outside estimate of a month.

Wattenburg said a four-lane bridge could be constructed with the flatcars, but he said Caltrans probably prefers, for safety reasons, two wide lanes.

He acknowledged, however, that there will be “a slight discontinuity” between the rest of the freeways and the flatcar bridge, so, he said, drivers will have to cut their speed.

As Caltrans began design work for the permanent replacements, many other highways, subject to flooding or landslides, were reopened elsewhere in the state, although access to the Monterey Peninsula remained cut off until at least today.

The main coastal route between Los Angeles and the San Francisco Bay Area, U.S. 101, opened completely. The last gap to be restored Sunday morning was a section between Ventura and Santa Barbara.

Meanwhile, Caltrans announced the reopening of California 46 between the central coast and the San Joaquin Valley. Closer to Los Angeles, the California Highway Patrol said it hoped to have Pacific Coast Highway through the Malibu area open in time for the rush hour today.

In Ventura County, authorities proclaimed that the danger of a new massive landslide or mud flow at La Conchita, where a precarious hillside had already smothered nine homes, had faded.

Sheriff’s and fire department officials Sunday withdrew a majority of their personnel from the community north of Ventura on U.S. 101.

“The imminent danger of the mud flow is gone,” said Senior Deputy Chuck Buttell of the Sheriff’s Department. “The threat of the mud coming down continues, but the flows that have happened . . . we’ve gotten a pretty good handle on that.”

Further north, in Monterey County, thousands of travelers were stranded by the raging Salinas and Pajaro rivers.

All of the major highways into Monterey were cut off: California 1, California 68, California 156 and California 183. By late Sunday, floodwaters had begun to recede and authorities hoped to reopen at least one route into the area.

However, a new storm was moving into the Bay Area more quickly than anticipated and rain had begun falling again in the hard-hit Napa and Sonoma valleys by late afternoon.

Most Monterey residents were taking their isolation in stride, but some travelers anxious to leave the region inundated the Monterey Peninsula Airport in hope of getting a flight out of town.

“We’ve got more problems here (in Monterey County) than I’ve ever seen,” said Al Friedrich, a spokesman for the county Office of Emergency Services.

More than 1,200 people were forced into shelters in Watsonville after the Pajaro River flooded the town of Pajaro and low-lying parts of Watsonville, officials said.

Along the swollen Salinas River, the town of Spreckels and parts of Salinas were evacuated in the early hours Sunday but most residents were allowed to return home later in the day.

Flooding was also reported in parts of Cambria in San Luis Obispo County, consistent with the pattern that the worst of the storm damage was in Central California.

Times staff writer Richard Paddock and correspondent Jeff McDonald contributed to this report.

* FARM DAMAGE: Storms took a heavy toll on agriculture industry. D1

* HERE COMES THE SUN: No rain lurks in Orange County forecast for this week. B1

* STORM DAMAGE: Ventura County officials begin to tally the losses. B1

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Flatcar Bridge

A bridge made out of railroad flat cars, with the whole cars as the roadbed, and cars sliced in half as the girders holding it up, will temporarily replace collapsed twin bridges on I-5 near Coalinga. The concept was developed after the Northridge earthquake, tested by Caltrans and will be used here for the first time.

SPECIFICS

* Typical Flatcar: 53’ x 10’6”

* Column: Cross-beam structure will support 420 tons

Source: Bill Wattenburg