This is one of the most flagrant examples of a speed trap I have ever seen. As the original comments say, it is a sudden 10-mile reduction in the speed limit. There is a sign, but the placement of the sign is (1) among much visual clutter and easily missed, (2) just as you have passed a busy intersection (where you need to be alert to cross traffic), (3) at the beginning of an unexpected curve, again, demanding your attention to the road and not a poorly placed sign, and (4) at the top of a downhill slope. The cop hides where he can zap you immediately as you pass the sign. There is no opportunity to slow from 40 to 30 even if you were aware of the sign. It would have been trivial to place a "reduced speed limit ahead" sign before the intersection, and to use one of those red-bordered signs to point out the place where the speed limit is reduced. If public safety is the goal of this reduction in speed (which is arguable), then these common-sense measures would have been put in place in order to better promote safety. The clearly minimal effort to alert drivers is a clear example of a revenue-driven speed trap.