MORE THAN a quarter million Bay Area commuters have had to find alternative routes to work because of the closure of the Bay Bridge. Two steel tie rods and a crossbeam from a steel saddle near the new S-turn broke and fell to the upper deck during the Tuesday evening rush-hour commute, rendering the bridge unsafe.

Fortunately, there are other ways for commuters to get to and from San Francisco besides having to drive many miles to other bridges. BART stepped up its service with more cars per train at several locations, and larger ferries were added to commuter service as well.

The bridge has been closed for brief periods, most recently over the Labor Day holiday weekend, to accommodate work on the new eastern section of the span connecting Oakland and Yerba Buena Island.

We hope that the latest repairs to the 73-year-old bridge will be sufficient to ensure safe passage until the replacement span being constructed alongside opens as scheduled in 2013.

However, the repairs made less than two months ago were supposed to have been sufficient, and they had been inspected several times since then by Caltrans.

Abolhassan Astaneh-Asl, a civil engineering professor at UC Berkeley who has studied the Bay Bridge for years, was critical of the repair, calling it a Band-Aid, and accused Caltrans of putting public relations ahead of public safety.

The latest incident comes 10 days after the 20th

Not long after, it was determined that the eastern section of the Bay Bridge should be extensively retrofitted to survive a major quake or replaced. The replacement option was chosen, but years passed before public officials could agree on a bridge design.

Then came a series of delays and increases in costs. The original estimate of $1.3 billion grew to $6.3 billion today, nearly 10 times what it cost to build a similar bridge in South Carolina in just four years.

Now, two decades later, Bay Area motorists will have to wait yet another four years before they have a reliable, earthquake-resistant bridge to use.

In the meantime, it is imperative that Caltrans closely examine the current bridge on a frequent basis to detect potential problems and fix them to prevent future closures or a major structural failure of one of the most heavily traveled bridges in the nation.

The latest incident should serve as a warning that constant vigilance is needed and perhaps spur a faster pace on finishing the replacement span that originally was supposed to open in 2006.