SAN FRANCISCO (AP) - San Francisco Bay Area commuters who have endured two major transit strikes in recent months were again scrambling to find an alternate way to get to their destinations on Friday morning after a computer problem shut down a major transit agency.

SAN FRANCISCO (AP) San Francisco Bay Area commuters who have endured two major transit strikes in recent months were again scrambling to find an alternate way to get to their destinations on Friday morning after a computer problem shut down a major transit agency.

Bay Area Rapid Transit agency trains were not running, and it was not clear when service would be restored.

"We don't have BART service this morning and we're not going to have service until further notice," BART spokesman Jim Allison told reporters at the West Oakland station Friday morning.

He added, "It's a huge inconvenience, we know, but we're just not able to run the trains with the computer system being down as it is."

Allison said in a recorded voicemail that officials had hoped to resume service at 5 a.m. PST, but were unable to meet that deadline.

The problem occurred shortly after midnight Friday, and affected 19 trains with 500 to 1,000 passengers. Allison said computer systems were not communicating properly with track switches that route trains properly.

BART is the nation's fifth largest commuter rail system and has an average weekday ridership of 400,000.

Commuters have endured two other BART service disruptions over the past several months as a result of an ongoing labor dispute. Workers walked off the job in July and again in October.

The shutdowns snarled the Bay Area commute, as people turned to crowded buses, ferries and roadways as alternatives.

BART's board on Thursday approved a labor agreement that ended the last strike, but removed a sick leave provision that was supported by unions.

The transit agency said the provision could cost $44 million over four years if one-third of union workers take six-week leaves each year.

BART officials announced last week that the provision had been inadvertently included in the proposed contract due to an error.

The decision created uncertainty about the fate of the tentative contract. Union representatives called the move an unfair labor practice and said they intended to discuss the matter with attorneys.