From NY Times article by Andy Newman:
"A native New Yorker, Mr. Walder, 52, was selected by Gov. David A. Paterson in July 2009 to run the authority, which operates the city's bus and subway systems and the Metro-North Railroad and the Long Island Rail Road. He will leave office on Oct. 21, the authority said"
Walder is leaving the MTA to take over the MTR Corporation, which operates a commuter-rail service in Hong Kong as well as intercity rail services between Hong Kong and Beijing, Shanghai and Guangdong, according to Newman.
Newman writes that some (Transit Workers Union Local 100, in particular) are happy to see Walder leave, while others praised him in public statements at the announcement of his departure.