Sorry subway riders, the Los Angeles County Metropolitan Transportation Authority is no longer operating on the honor system.

The turnstile gates for the Purple and Red lines at Union Station will be latched today and riders will need a TAP card (Transit Access Pass) -- with the $1.50 fare loaded onto it -- to gain access the subway. The card costs $1 and can be reloaded so riders only need to purchase it once.

For the most part, Metro has been trusting its customers for years, with subway turnstiles allowing riders to pass through without paying the $1.50 fare. Los Angeles County sheriff’s deputies only sporadically sweep subway stations checking for fare evaders.

The Union Station turnstiles are the first to be latched by Metro. The 15 other Red and Purple line stations are expected to follow by the end of the year. Metro officials estimate the increased accountability will bring in an extra $6 million to $9 million in annual revenue.

Last year, county Supervisor Zev Yaroslavsky said one reason Metro officials failed to lock the gates sooner is because they were operating under the false assumption that only 3% of riders were evading fares.

But during the fall of 2011, Metro staff tested locking gates at 10 stations and reported increased revenue at the 7th Street/Metro Center and North Hollywood stations by 18% to 22%.

Riders who are caught not paying the fare could receive a $250 ticket.

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Joseph.serna@latimes.com

@josephserna