The man credited by many for expanding and modernizing Long Island Bus and guiding the system to its highest ridership is retiring, MTA officials announced Thursday.

Joseph Smith, 55, president of the MTA Bus Company and Long Island Bus and senior vice president of New York City Transit's bus department, formally resigned in a letter sent to MTA Board members on Wednesday.

He said in the letter that he was stepping down "with mixed emotions," effective Dec. 30, "to devote all of my energies to my family during a critical time."

Smith, who according to state records made $269,365 last year, joined the MTA 33 years ago - originally working as a bus driver out of the defunct Amsterdam bus depot in upper Manhattan, MTA officials said.

"Joe exemplifies the hard work, dedication and innovation that exists throughout the MTA," said MTA chairman Jay Walder.

Smith climbed through the ranks of the MTA's three bus systems - New York City Transit, MTA Bus and Long Island Bus. And when the three operations were consolidated in 2008, Smith was chosen to lead them all. That same year, LI Bus carried a record 32.6 million riders.

As head of Long Island Bus, which is owned by Nassau County but operated by the MTA, Smith helped navigate LI Bus over some fiscally bumpy roads, as the MTA and Nassau have warred over who is responsible for funding the agency. The MTA has said it will no longer make up for Nassau's $26-million shortfall, and Nassau is looking for a private operator to run LI Bus.

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