Yeah it seems silly to sit in the median with a radar gun...I don't think I've actually ever seen a cop do that.
They do that here all the time. Between Lincoln and Omaha, where there's a TON of interstate traffic, I can think of about half a dozen places where it's more surprising not to see a cop than to see one, right there in the middle of the road. Usually they're parked in the emergency corridor between the two lanes, but I've frequently seen them in the grass in the regular median. I just saw one last week in the grass on the median of the highway heading out of downtown Lincoln on my way home, as a matter of fact.