In this version of the Pile Driver, the performing partner positions themselves perpendicular to their partner, who is engaged in a deep forward fold beneath them. The partner doing the thrusting ought to be fit enough to repetitively perform the mini squats illustrated; leg and abdominal conditioning will improve the execution of this pose.
In order for Overpass to be comfortable for the receiving partner, they too must be equipped with muscle strength, agility and flexibility. This inversion can be physically exerting, so it's recommended that you practice it on your own before having sex in it. Get a good warm-up before you engage and don't forget to stretch before and afterward!