Fraud involving Clipper cards has skyrocketed after reports exposed a loophole in BART’s fare payment system in November, resulting in more than $170,000 in lost revenue.Under the current system, BART passengers who use a Clipper card can pay as little as $2 to travel anywhere in the transit network. But almost any trip on a $2 ticket results in a so-called negative balance. For instance, traveling from downtown San Francisco to San Francisco International Airport costs $8.10. Read More