Additionally, even if the speed limit is changed, assuming there is appropriate signage it is your responsibility to follow the speed limit.
https://www.al.com/news/2022/01/police-in-this-tiny-alabama-...
https://reason.com/2022/05/08/11-insanely-corrupt-speed-trap...
https://www.cbsnews.com/news/speed-trap-profits-could-come-e...
> Waldo, Florida, is just two square miles, and Highway 301 runs right through the village, but the highway speed limit changed six times, enabling police to write thousands of tickets a year. The AAA put up a billboard warning drivers.
It's the responsibility of town planners, etc. to design roads and their speed limits for safe traffic flow. Sudden speed limit changes are dangerous, and a much safer approach - if, say, a highway runs through a village for two miles, with multiple junctions - is to have a single speed limit for the entire stretch. Not to have speed ups and slow downs, aggressive enforcement, and evidence that the majority of your village's funding comes from fines. That is municipal malfeasance.
https://www.propublica.org/article/fenton-louisiana-brought-...
That's not how driving actually works in practice. Most of the time drivers rely on a learned sense of what the standard speed limit is based on the type of road. E.g. highways are 65 - 70, major roads are about 55, neighborhoods are 25 - 35, etc. When I learned to drive, the state's drivers manual literally had a section on what speed limit you should assume on different types of road if you haven't seen a sign.
That's to say nothing of situations where the sign is actually hidden. For example, I was once pulled over on a road that abruptly dropped more than 25 mph, on a significant downward slope, where a tree was growing in front of the speed limit sign.
Speed traps are as described by others: abrupt, significant changes in speed limit with minimal warning and poorly-visible signage.
Look up the story of Waldo, Florida, which for years and years did this on US 301. The town lies on the main route between Gainesville, location of the University of Florida, and Jacksonville, where it meets I-95 and thus access to points north along the East Coast. It was one of the few places that the American Automobile Association would directly call out as a speed trap.
I know that Alabama has had a series of laws starting in the 90s passed by the state legislature to rein in such activity. Not entirely successful, but not without its victories, either.
This has to be legislated at the state level, though, or the municipalities will go wild in their policing for profit.
The south catches a bad rap for speed trap towns but seems like every 10yr or so some town in the midwest abolishes its police department or something because of that sort of behavior.
In principle, great, but the trick is that the signage is such an inscrutable combination of badly placed adhoc signs and road-markings that a huge number of visitors with zero intent to breach a rule get fined.
There is a common sense principle such things should meet: if the revenue from a traffic measure is high and consistent then not only has it failed in it's purpose to change behaviour but there is something bogus about it's setup.
A judge first ruled the signage was fine but after seeing so many appeals, he admitted he had been definitively proven wrong and it needed to be improved.
Legally, of course. But there is such a thing as an artificially low speed limit. If the road conditions allow driving in safety at 60 km/h but a town installs a sign that says that you have to drive at 10 km/h, with no pedestrian traffic or bends or anything at all that could justify it, then that is a speed trap, and drivers who drive the normal speed of 60 on that stretch are not doi g anything wrong, the law is just being abused against them.