I remember hearing of a tiny town near a main highway that annexed a couple hundred yards of the highway so they could drop the speed limit and have a officer there writing tickets. I can't remember what was done to limit that.
You may be talking about Estelline. It's a semi-ghost town on US 287 about two hours southeast of Amarillo. Drove it many, many times growing up.
Entering town from the east you crest a blind rise to face a sudden speed limit drop and hard curve. Speeds used to drop from 75, to 45, then to 35 without warning, and in a matter of a few dozens of yards. You could, quite literally, be standing at one limit sign and hit the other with a poorly-thrown rock. Unless you were on the binders hard enough to break traction, there was absolutely no way to get slowed down. There was always a city cop there, ticket book in hand. No leniency, no leeway, and no exceptions. They were famous for their 1 mph-over tickets.
I think Texas got tired of the notoriety and now requires a combination of "Reduced Speed Ahead - XX MPH" signs and minimum distance between speed limit changes, at least on TXDOT-maintained roadways. It seems to be calculated on enter/exit speeds because it's been years since I encountered speed limit changes requiring much more than just letting off the gas and coasting down.
*edit to add* I found a 2019 Texas Monthly article that still shows Estelline is collecting sizeable revenues from tickets. Guess they're still up to their old tricks. Texas law limits the amount of ticket revenue municipalities can retain. However, it's calculated in percent of total gross ticket revenues so they just make up the difference in volume, I suppose.
Brad