How does this form of fare evasion work? I thought a rider usually scans/tags a form of payment before boarding the train and does so again after disembarking.
Yes, you scan or insert your card when entering the station from which you are departing and then scan again when exiting the destination station. But you are only charged on exit because the fare is calculated based on the distance between stations. If you go through the emergency exit at the destination and thus avoid scanning your card, you can skip out on the fare.
They have emergency exits in most public transit systems, but usually they have some sort of alarm that sounds when you open it. But the BART emergency exits are literally just a swiveling door. If there's no attendant, you could literally just walk out of it without attracting much notice. I've seen people do this multiple times. I don't know why the BART authority considers this acceptable. I suppose they can catch offenders if they notice that the card is always used to swipe in but never to swipe out.
They have emergency exits in most public transit systems, but usually they have some sort of alarm that sounds when you open it. But the BART emergency exits are literally just a swiveling door. If there's no attendant, you could literally just walk out of it without attracting much notice. I've seen people do this multiple times. I don't know why the BART authority considers this acceptable. I suppose they can catch offenders if they notice that the card is always used to swipe in but never to swipe out.