It is a common sight on American highways. You are driving down a highway with, say, a 55 mph speed limit, and upon entering a town it rapidly drops to 45 or 35 mph. Then right around the next corner a local law enforcement officer with radar is there ready to ticket you if you fail to slow down in time, otherwise known as a "speed trap". And often the fines for these violations, even for going a mere 5 mph over the posted limit, can be several hundred dollars, and often much more for going faster.
For municipalities (such as some in Louisiana, in my experience), I assume this is a major moneymaker, bringing in revenue to towns that otherwise have few sources of revenue. (for example, fines in Baton Rouge and New Orleans are much lower than those in smaller towns in the state) Through the use of speed traps, citing drivers for going very little over a posted limit, and charging exuberant fines, this could in effect be seen as a ploy more intended for generating revenue than for ensuring traffic safety.
Could abuse of speed limit statutes by a municipality (or parish) for the purposes of making money ever result in punishment or other legal ramifications? Or would it be up to a legislature to regulate the enforcement of speed limits?
(But at the same time, I bet there are few state legislators willing to pass a law that would eliminate massive streams of revenue for their district, especially when most of those being fined are passing motorists not within their voting constituency.)