Officer parks in drivway at bottom of low hill and shoots radar north east at the crest of the hill. Near the crest of the hill travelling south west, the road widens noticably. Beyond the hill (to the south west) is a wide, straight strech of roadway. The speed limit changes from 30mph to 40mph 3/4 of the way down the hill, above the officer. The 40mph sign becomes visable before the motorist clears the hill. Citations are issued for speeds exceeding 30mph comming down the hill, even though the speed limit has increased to 40mph before the spot where the officer is parked.