My very spread out city has two roads between its southern suburbs and the city, each is about 30km long
Both only have speed cameras to control speed
So most people drive at what their car tells them is the speed limit, which almost always is 5km/h slow, then a few follow of public safety advice and drive 5km/h under the limit, so actually at -10 and very few have accurate speedometers or GPS that tells them their actual speed and try to travel at the speed limit, and a small number deliberately speeding
Then when we reach the speed cameras the cars going slow all slow more, the speeding cars slow down to well under the limit, and the very few confident drivers try to continue at the limit
Traffic is really smooth and will behaved before the speed cameras, and a hundred metres after them