It's a randomly placed object. It seems to be placed only on straights, so you need a straight that is long enough to fit it (it doesn't have to be of the type "straight" though, it could just as well be a "curve" that is straight), and a bit of luck. Stay away from areas marked as forests and mountains, as they will usually spawn trees and rocks along the track. I'm not sure what the city areas do.
Also make sure that your road doesn't cut through the terrain too much, as that usually spawns the "house on top of a hill" prop. So place the two anchors on a somewhat equal level to maximize your chances.