(Old news to many, I know, but I didn’t get around to uploading the pictures yet!)
A few weeks ago there was a big outdoor scene at the green screen sound stages of the Michigan Motion Picture Studios in Pontiac. Helicopters were seen overhead, and generally there was a lot of noise and smoke and maybe fire. Extras were dressed as police and first responders. I saw these vehicles (below) and was a little confused. It takes me a while to catch on. Clearly these are DC vehicles, so the scene that was filmed was not set in either Metropolis or Gotham as previous scenes had been.
Fast forward a week or three and several yellow DC cabs are seen on the filming lot at the Wayne County Courthouse in downtown Detroit. Along with a DC Metrobus. Aha! During the Huge Detroit Flood of 2014, a few scenes were also filmed at the Detroit Library and Wayne State University, and it’s suspected that part of these scenes were made to look like the offices of the FBI in Washington DC. So there you go.
This was all explained more clearly by Chris Begley at Batman News!