Then it wasn’t a speed trap. Just running radar is not a speed trap, it’s enforcement.
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.