Sometimes the cop cars are parked there without a cop in it.

Saves costs for the department, and gets people to slow down.

Some other states have even put dummies or mannequins in the cars to make it look like a more real possibility and get drivers to slow down, without dedicating an officer to tickets.

Also smart departments are probably avoiding traffic citations, because these always turn into national news when they "accidentally" use the gun instead of the taser on someone. Departments are probably better off dedicating officers to "real crimes".