Orange County Freeways Called Relatively Safe : Design: Experts feel comfortable about the safety of elevated highways. But without modifications, pillars and columns appear to be the system’s weak link.

Unlike in the Bay Area, where a double-deck freeway became a single tier in Tuesday’s massive temblor, there are few places in Orange County where ribbons of concrete overlap and leave the roads vulnerable to collapse during a major earthquake, officials said Wednesday.

But while most of Orange County’s older freeway overpasses and other elevated structures have been retrofitted to minimize possible earthquake damage, the modifications will not be complete for about three more years, state highway officials said.

Frank Weidler, Caltrans deputy director for construction, operations and permits in Orange County, said the work remaining to be done involves reinforcement of the pillars or columns that support the concrete spans.

It is that part of the structure--the support pillars--that appeared to have failed in the collapse of the Nimitz Freeway--I-880--in Oakland, where more than 200 people are believed to have been crushed. The mile-long section of the Nimitz Freeway that collapsed was double-decked and the upper level fell onto the cars traveling on the lower level.

“On balance, I feel fairly comfortable” about the safety of elevated freeway structures in Orange County, Weidler said. “I feel pretty good about what we have down here. . . . We have no viaducts, no double-decked structures--nothing where there’s a roadway up for a prolonged length.”

Weidler said, however, there are 488 bridges and overpasses in Orange County.

“We do have some freeway-to-freeway overpasses and connectors,” he said. But he added that the modifications “are moving forward.”

Weidler said the county’s largest interchange is between the cities of Santa Ana and Orange where three freeways come together--the Santa Ana, the Orange and the Garden Grove.

There are more than a dozen ramps connecting the three freeways, many winding like spaghetti under, over and around the others.

The other major interchanges Weidler identified were the San Diego Freeway connections to the Santa Ana Freeway near El Toro and to the Newport Freeway near Tustin.

Since the San Francisco and Bay Area earthquake, county officials also said Wednesday that they will be reviewing the earthquake protection built into several street bridges that pass over the Santa Ana River.

Bill Zaun, the county’s director of public works, said there are 11 older bridges in particular that will be reinspected to be certain they are properly supported.

He said the county has built 21 bridges over the river in the last 40 years, 16 of which were done before more stringent earthquake construction standards were required in 1971.

Five of the 16 older bridges have since been retrofitted with additional support for earthquakes. He said he was uncertain whether the others lacked the support or did not require it, but he added that those bridges would be reviewed.

He said he could not identify which 11 are to be reinspected.

Caltrans’ Weidler said almost all of the county’s freeways were built before the standards changed in 1971 and so most had to be retrofitted. He said the first phase--which required the spans to be fitted more securely to the pillars--has been completed.

The second phase involves reinforcing the pillars.

The other considerations for damage to freeways in an earthquake include the type of soil in which the structure is anchored and the location of the nearest fault.

In a study prepared by local authorities about the effects of a major earthquake on the Newport-Inglewood fault that extends through Orange County, officials concluded that the greatest damage would be done to the freeways nearest the coast--the Pacific Coast and Coast highways and the San Diego Freeway.

The Santa Ana Freeway, it said, should “provide an alternative north-south corridor east of the zone of high-intensity shaking.” It also said there should be “numerous alternative surface streets which can be used to bypass damaged portions of freeways.”