Many years ago we used discarded escalator handrail. At the time, it was free for the taking whenever the local escalator service company replaced worn handrail (which was quite often). I don't know if they recycle the stuff now, or still just throw it in the trash.
The handrail was heavy, so it didn't move too much, but still had enough give to absorb some impacts. One nice thing about it was that it was easy to form sweeping corners, as opposed to straight lines and sharp corners like with 2x4's. But it did need to be faced with some type of thin plastic, since tires had good traction on it (when a car brushed the wall, it wouldn't slide off, it would just stop dead).