What has worn the roads "about the same" (line 10) in the "The Road not Taken"?

In Robert Frost's poem, "The Road Not Taken," the speaker considers two roads and must choose one. As he's trying to decide, he looks at them and really thinks about it. The complete line is, "Though as for that the passing there/ Had worn them really about the same." While the speaker doesn't explicitly say what has worn the roads the same level, it can be understood that other people had walked down the roads before the speaker. The road he decides to take has really been walked on or worn by other walkers as much as the other. 

This is an important line because it suggests that other individuals much like the speaker have stood at that fork in the road and made the decision to choose one over the other. When the speaker says they were worn about the same, this means that either road would have been a fine choice. One was not better or worn more than the other. The larger point, then, if the road is a metaphor for choices, is that it's not always clear which choice is better than the other. Sometimes neither choice is--you just have to make one.