The traffic on Flatbush was relentless. It was hard to imagine how a Saturday afternoon arena event could be accommodated unless there were significant changes to the area transportation system, beyond the mitigations--among them a free MetroCard (for basketball games, not concerts) and shuttle buses (ditto)--planned as of now.
Also, though the alternative UNITY plan Shiffman helped develop calls for a park on the triangular plot opposite the garden, between Flatbush, Fifth, and Atlantic avenues, it sure didn't seem like that salubrious a place to gather, given the traffic on Atlantic as well. Many of the major transportation changes that are proposed in the UNITY plan would have to be implemented, at the least.
Remember, the Empire State Development Corporation (ESDC) rejected several suggestions from Borough President Marty Markowitz about addressing traffic and transit issues. There was more criticism, from consultants Brian Ketcham and Carolyn Konheim, and the ESDC's not-quite-response.