The A.V. Club’s Mike D’Angelo on that car chase from The French Connection:
Early in the scene, it’s mostly Hackman (who later became a mildly successful amateur race-car driver) behind the wheel, clearly visible either in profile or in the rear-view mirror. But the second half features footage shot from the front bumper, and that’s Hickman (“Hickman, Hackman. Hackman, Hickman”) barreling down actual, non-staged Brooklyn traffic at what Friedkin, who was operating from the back seat, claims was upward of 90 miles per hour. Some sources—notably cinematographer Owen Roizman—claim this is exaggerated slightly…you can still tell that what you’re seeing was in no way safe, and the idea that most of those other cars are just ordinary folks going about their day is mind-boggling. Do they even know they’re in the movie, or do they just think they narrowly avoided being hit by some random asshole?
I had no idea. Crazy stuff.