Well, I had to get creative to fit the turn arounds where I did, but you don't need a lot of space. You need a minimum of about 15 inches width. A 12" diameter curve (measured in the center of the road, where the iron wire is buried) is about the sharpest I would try with O-Gauge, and I actually got managed to fit in 17" curves at both ends (20 inches from outer curb to outer curb on mine. .Nice work Lee. I thought about this for my railroad too, but I have no turn around area.