Starting Wednesday, Transformers 4 will arrive at the "Chinatown" set in Detroit for 7 days (July 31-August 8). The set is really shaping up with a ton of destruction and devastation. An interesting find is that one of the subway cars nearby reads "transitchicago.com". This really makes no sense to me since there are signs everywhere for Vogue, Victoria's Secret and more which have Chinese writings on them, so a simple Chinatown within Chicago doesn't seem too plausible in my opinion. The subway car also could just be there for a small scene in the somewhat immediate area.
Also, filming has just wrapped up in River Rouge, Michigan, where explosions were set off on top of two old ferry boats. The ship keeper said that one of them will have a very prominent role in Transformers 4.