Great movie and gret chase scene besides Steve McQueen’s Bullit movie ! Funny the movie was filmed after the original Mayor Daley went for a dirt nap !
IIRC, the producer or director complimented mayor Jane Byrne for being highly cooperative in getting them permission for all the city scenes.
We were on our way to visit relatives in Wauconda and had to take a big detour because they were filming that notorious highway pileup on Route 12 right south of town.
The original Daley didn’t like filmmaking in the city at all. He rarely gave permission.