BART riders -- and especially those who take the system's Warm Springs and Dublin/Pleasanton lines and the Oakland International Airport connector -- here's an important heads-up: You'll see major changes in service and can count on delays during the Labor Day weekend.

That's because BART, as part of the system upgrade program financed by last year's Measure RR, will be replacing tracks and electrical equipment in downtown Oakland starting early Saturday morning.

Direct service on BART's Warm Springs and Dublin/Pleasanton lines will be replaced by a "show up and go" AC Transit bus bridge operating between West Oakland (for passengers traveling to and from San Francisco) or 19th Street (for passengers traveling to and from Richmond, Berkeley or the Pittsburg/Bay Point line) and Fruitvale Station. The buses will be free for those who have BART tickets.

Lake Merritt Station will be closed throughout the holiday weekend.

BART says passengers should allow 20 to 40 minutes extra for trips to and from Warm Springs, Dublin/Pleasanton and Oakland airport. Service on the system's other lines -- from Millbrae to Richmond and San Francisco International Airport to Pittsburg/Bay Point -- will not be affected.