system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 How does traffic work in movies ?

Like I know on residential they can shut down the block to film what they want. 

Generally speaking do they pay extras to drive around the scene to create traffic flow ?

And scenes on the express way are they extras driving those cars.
gpt
Sometimes the vehicles are actually going down a street and following the traffic. A stunt driver could be placed on top of the car, driving for them but out of camera view to the actors “driving”. And sometimes the entire car is on a trailer pulled behind a truck with camera crews at all angles filming as they drive down the street. You’ll occasionally see them with police escorts in LA.