I believe a Statutory Road Association can likely own "common land" but I would recommend against it. The Statutory Road Association should focus entirely on management of the road and its maintenance. That by itself should be enough to keep the Officers and Directors busy. As I recall when I (as Road Commissioner) researched liability insurance to cover our Association including Officers & Directors the annual premium cost was less because our Association owns absolutely nothing. It appears to me that any "common land" would provide additional risk and I am pleased we own none. I do recommend that you continue to form a Statutory Road Association but let the ownership of the common land be managed by some form of what you call a Voluntary Association.