I think there is a sense in which the way that the title focuses on the road NOT taken helps highlight the sense of loss or nostalgia for other possible futures that the paths we take in life and the choices we make preclude. This is the focus of the last stanza, to my mind, as the speaker looks back on the lives he could have had with regret or at least curiosity.
I find it a great way to symbolize the idea that our life follows a pathway, or road. The decisions we make regarding how to act during our life really do become choices of which road we will travel along the way. As a confirmed individualist, I identify with the title.
I agree that the title of the poem generates curiosity. Immediately, I am curios as to why the road has not been taken. What is it about the road which makes it this way? The road does also bring to mind the decisions of the past and why one did not choose to take the road. Many times in life people look back and wonder "what if."
Indeed, this title generates curiosity. As the speaker deliberates upon which road to take, there is a suggestion of the indecisive mind that will forever worry about the what if's of life. When he does choose one--no matter which one it is--he will always wonder about and perhaps rue the one not taken. Thus, the obsessive mind deliberates and recalls always "the road not taken."
The title of the poem creates immediate interest and curiosity. We wonder, just from reading the title alone, what kind of road the title refers to (will it be literal or metaphoric? if metaphorical, metaphorical in what way?), whether the poem will be about the road "not taken" by the speaker, whether the poem (alternatively) will be about the road he did take, or whether the road the speaker did take is the road "not taken" by most other people. In short, even the title of the poem is suggestive and ambiguous, like the poem itself.
It is always an interesting concept to think about the primary focus of the poem, which is the path the author chooses, and the title, which is refers to the other road--the "might-have-been" path. Note, too, that the descriptors of each path are virtually the same. The point, of course, is that each road we takes is the path we must live with in life.
The title implies that what was not done was as important as what was done. It implies that the things that we give up when we make a choice (the roads we don't take) are just as important as what happens on the roads that we do take.
Literally, it refers to the road that the narrator took, grown over and unused. The concept is that the unused road might be more interesting than one that everybody uses.
More abstractly, it refers to the path (in life) not taken, or the choices one makes. British author Terry Pratchett uses a concept in his stories called the Trousers of Time: a fork in your life where your choices diverge; take one, and your life is irrevocably changed.
...[I] looked down one as far as I could
To where it bent in the undergrowth...
This could mean that, confronted with a choice, he considered one as much as possible before taking the other; one choice may have been safer, but he took the "one less traveled by," or the choice that others may not have taken.
The title of this poem is a clear statement of its subject -- it implies two roads and the decision that has to made at the fork in the road. Everyone is confronted with decisions every day. Some are minor with little long-term consequence, and others are momentous and have long-lasting effects. When we make big decisions we always weigh each side, and even after having made the decision we have the temptation to look back or second guess our decision and think "what if" about the road not taken. Those are the sentiments of the speaker of the poem.
I think that by choosing the road "not taken" as the title, Frost focuses us on the road that no one else took. You could also look at it as the road that he did not take. One of the things I like about this poem is that it is open to interpretation.