In the city I grew up in (Edmonton, Canada), the police used to tell the radio stations where the radar traps were. The goal of a radar trap is to get people to slow down.

That was in a gentler time; nowadays I recognize that radar traps are often used for revenue generation, so forces might be more reticent about revealing location. But 20 years ago even the police themselves would have had no issue with this, and might even have endorsed it.