New York City subway and bus fares would increase by 50% by 2023 if the Metropolitan Transportation Authority continues its pattern of 8.4% fare increases biennially, according to the Independent Budget Office.

Under this scenario, the current $2.50 base fare would reach $3.75 in 2023. In inflation-adjusted 2013 dollars, that would be a base fare of $2.87, the nonprofit watchdog agency said in a report compiled for the Straphangers Campaign ridership lobbying group.

"Given the financial pressures the MTA will face over the next decade, some fare increases are likely. The timing and amount of those increases, however, may be very different from those analyzed here," the IBO's Alan Treffeisen wrote.

In 2009, after then-Gov. David Patterson and the state legislature authorized new sources of revenues, the MTA initiated a series of biennial toll and fare increases.

The MTA, with $32 billion of debt, is one of the largest issuers in the municipal marketplace. Moody's Investors Service rates the authority's transportation revenue bonds A2, while Fitch Ratings and Standard & Poor's rate them A.

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