You can always do what a old neighbor of mine use to do. Have cars parked normally in drive way and have a basket of balls ( beach, volley or basket balls) and if you see someone speeding just roll the ball towards the road as they near. Mind you she sat in a protected area that wasnt easily visable from the road.
When I first noticed her I was walking buy and she had a wire bin of balls near her porch. Sure enough car would occasionaly screech to a stop. Now if only she had a neighbor accross from her to throw them back, she wouldnt have to go up to the ditch later and collect them.
