BAY AREA QUAKE : End to Freeway Double-Decks Urged : Transportation: The Nimitz highway collapse raises questions about the design used to increase road capacity.

Ambitious plans to double-deck much of the Los Angeles-area freeway system suffered a severe blow when nearly a mile of the double-decked Nimitz Freeway--Interstate 880--collapsed in Oakland in Tuesday’s earthquake, killing scores of people.

Los Angeles County Supervisor Kenneth Hahn on Wednesday called for a halt to the double-decking now under way on the Harbor Freeway, near downtown Los Angeles, while Assemblyman Richard Katz (D-Sylmar), chairman of the Assembly Transportation Committee, said the Nimitz collapse “raises legitimate questions about double-decking of freeways.’

William E. Schaefer, chief engineer for Caltrans, said in an interview that the Nimitz disaster should not affect future double-decking plans because “the newer designs don’t present that kind of problem.”

Schaefer said the portion of the Nimitz that fell in was built in the early 1950s, but that a newer stretch of the same freeway, a few miles south of the collapse, survived the earthquake without damage.

“When you do it from the beginning, it’s not a problem with today’s technology,” Jim Gates, Caltrans senior structural engineer, said after he and other Caltrans officials made a Wednesday afternoon presentation to the California Transportation Commission in Sacramento.

But double-decking clearly is in trouble, whatever Caltrans officials may say.

Gerald Silver, president of Homeowners of Encino, said his group and other homeowner organizations are “bitterly opposed” to double-decking and will “do whatever is necessary to make sure this doesn’t come about” in the San Fernando Valley or elsewhere in the Los Angeles area.

Caltrans officials believe that adding a second deck to existing freeways offers a partial solution to the increasing traffic congestion in Los Angeles and other urban areas in the state.

“We’re running out of room, we’ve got to do something,” Jerry B. Baxter, Caltrans director in Los Angeles said a year ago in announcing plans to double-deck 2.6 miles of the Harbor Freeway.

Baxter said that Caltrans already has narrowed traffic lanes, eliminated shoulders and initiated complex “traffic management” plans but that urban congestion still grows ever worse.

In addition to the Harbor, the transportation agency also is considering double-decking parts of the Santa Ana, San Diego, Santa Monica and Ventura freeways.

But critics say double-decking would increase noise, vibration, air and visual pollution and, most of all, would present serious hazards during earthquakes.

The earthquake argument took on added force Tuesday, when columns collapsed and the upper deck of nearly a mile of the Nimitz Freeway, a section known as the Cypress Viaduct, fell onto the lower deck.

Like every bridge in the Caltrans system, the Cypress Viaduct had been “retrofitted” after the 1971 earthquake in the San Fernando Valley caused several freeways to collapse.

But Schaefer said Wednesday this $54-million retrofitting program only solved the problem of lateral movement--deck spans slipping off their supports, as they did in the 1971 quake.

In a second phase of rehabilitation. Caltrans is placing steel wrapping around the bases of elevated freeways that are supported by single columns. That will cost $65 million.

But the Cypress Viaduct is supported by multiple columns and, Schaefer said, “we really don’t have the expertise to know what to do” to fix these.

Research is under way at UC San Diego on the best way to retrofit an elevated freeway like the portion that collapsed but it will take at least a year to find a solution, Schaefer said.

In addition, a a blue-ribbon panel of international bridge engineers will be asked to study the problem.