If you ride a lot of paths, you will quickly notice that some bollards are well-designed to be highly visible, and others are really just accidents waiting to happen. I even know of a path where the bollard was removed, but a 5 inch tall metal base is still there smack dab in the middle of the path just waiting to grab a tire.

The better ones are tall and wide enough to be seen even in path traffic, brightly colored, and ideally preceded by a warning sign or road mark. The worst ones are short, unpainted wood, concrete or metal that just stick up inconspicuously from the pavement. There's no justification for that, and lack of visibility pretty much defeats the purpose of the things.