Q: Last Monday I entered my subway station on the way to work and realized I had forgotten an important book. I went home to get it and then got back too soon, apparently, to reuse my 30-day unlimited Metro-Card. Why does the MTA make us wait to reuse it – and why exactly 18 minutes?

A: The delay was put in place to prevent fraud. If there were no delay, a rider could swipe all his or her friends through, and people would stand at the entrance asking a quarter a swipe for entry. Pandemonium surely would ensue. So there must a delay of some kind.

The choice of 18 minutes results from the New York City Transit accounting system. Basically, NYCT likes to work in 10ths of an hour. Six minutes represents a 10th of an hour; 18 minutes represents three-tenths of an hour. The reuse time applies only when riders are trying to get back into the same station. The turnstiles for any given station are networked together, and they record the last use of the MetroCard. If a rider walks over to another line or takes the bus, the card should work with no problem.

Back in 1998, NYCT claimed that 18 minutes was the shortest lockout period its software could handle. According to the minutes from an April 1999 City Council Transportation Committee hearing, NYCT promised it would eliminate, or at least shorten, this period at a later date.(The minutes also show the MTA employee lockout period is only six minutes.) Clearly, the software issue was long ago resolved, but no change has been made.

NYCT has since told the City Council and consumer groups that it doesn’t want to change the reuse delay because a shorter lockout period of 12 minutes would be less effective at stopping fraud.

That’s disappointing, because 18 minutes is plenty of time for an honest rider to leave the subway, run a quick errand, and, upon returning, have to stand around waiting for his or her card to refresh.

On the other hand, a 12-minute lockout period allows an unscrupulous swipe-seller a maximum of 120 swipes a day. If this villain sells each swipe for the $1 that I’ve seen them charging, he could gross $120 a day. So he makes $113 after purchasing the unlimited one-day pass – if he never stops to sleep (for more than 11 minutes at a time) or eat, and he never gets caught or has to flee his spot. And beware: If you get caught buying a swipe, the fine could cost you more than $100.

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