121 Highway going north past McKinney and Lewisville exit split; as Hwy 121 turns into 121 bypass into Coppell. Police hide around corner or underpass; motorcycle and SUV; 55 mph speed limit not posted; unfair as you are driving downhill and speed limit is difficult to monitor around turn; sudden braking may cause an accident to reduce speed; Simple solution is to post a sign and warn drivers rather than take advantage of road conditions to issue tickets.