I cannot place American accents particularly well, so this is not intuitive to me based on watching the Christopher Nolan Batman movies.
Do the cast use a particular accent to place themselves in the (fictional) Gotham City? Certainly Gary Oldman, who is from London, England, would have to deliberately affect an accent of one kind or another. Is there any evidence that a particular accent was chosen or synthesised to represent Gotham? Would this be obvious to U.S. natives where Gotham is supposed to be?