As you come into Post off I-84, heading North, the speed limit drops from 75 to 65 to 55 mph in a span of less than a quarter of a mile. This happens just as you are coming across the viaduct into town & the signs are on the downhill & outside, ( So it is easy to miss them), The viaduct is slightly spiraled & as you come to the end of it the county Sheriff is parked at the base of the bridge. I was in the inside lane & there was a row of Semi trucks in the other, I did not see the signs at all. I have a good radar detector but because the Sheriff is parked at the base it didn’t register until I was right on top of him.