Other deficiencies had not been addressed, however, and while the Embarcadero Freeway did not collapse, severe damage ultimately resulted in the freeway's demolition. None of the collapsed structures, all designed to pre-1974 seismic standards, had been recently retrofitted. In reviewing these failures, engineers observed some cases where a recently retrofitted bridge adjacent to a collapsed bridge did not have any discernible damage. Replacement bridges for the five collapsed structures have been designed to current seismic standards. As is customary for most building seismic retrofits, the objective for the California highway bridge seismic retrofit program is to prevent collapse.
Damage control is sought on an incremental basis considering the tradeoff between cost and function.
Bridge engineers were aware of the seismic vulnerability of some of the collapsed bridges, in particular the Santa Monica Freeway, which was identified for retrofit. Seismic retrofits for some of the other vulnerable bridges were being designed when the Northridge Earthquake struck. Despite extensive bridge failures during the Northridge event, none occurred in newly designed or recently retrofitted structures, even when these structures were subjected to similar motion intensities as the collapsed bridges. The current bridge seismic retrofit program therefore appears to be successful. The California highway network comprises approximately 20,000 bridges of different construction types and vintages.