The San Francisco Chronicle details the problem in BART has New Problem: Old Tracks. 

 The nearly half-century-old system needs to replace its worn steel rails and cross ties. The problem has produced derailments, a drop in train speed in several trouble spots, and a repair schedule that will close the tracks in Oakland over an estimated 11 weekends. 

Track maintenance is nothing new for transit systems as equipment and track wear out. But the scale of the problem and BART's essential role in carting nearly 400,000 daily riders to work, school and appointments make the task important. It's imperative that the system focus on improving service as quickly as it can — or risk public concerns about safety and reliability.