As a tipster noted, Streetsblog came out with a detailed story yesterday about Clipper's "Dirty Little Secret," in which enterprising BART riders can scam a free trip (after adding the minimum $2 fare to your card) from one end of the system to another and back. KRON's Stanley Roberts inadvertently discovered this Clipper quirk, among many others, a couple of weeks ago.

Apparently, Clipper allows riders to go below the card balance by $10 (depending on where their destination is once they've gone past $0), so they're able to exit the system at stations that don't have add-value machines. Since users currently aren't required to pay a fee or register their cards, it's easy enough just to ditch the cards after you've hit the negative balance.

Of course, the taxpayer ends up footing the bill for this, as Metropolitan Transportation Commission (MTC) pays for these negative balances using regional funds allocated to the Clipper roll-out.

MTC didn't want to pay to retrofit BART stations with Add-Value machines, which would have been the obvious solution. Another option is to require riders to register the card or pay a fee before they can "go negative."

The thing we dislike most about Clipper -- aside from its grating sound effects -- is the fact that it takes 72 hours for funds to take effect when added online. In this day in age, there just isn't an excuse for this. As Steve Rhodes notes, the Clipper advertising is very misleading with regard to this flaw.