There are at least three possibilities as to who the speaker is in the poem.
Because the speaker always says "I," many people have believed that the speaker in the poem is Robert Frost himself. However, the poet himself often said that the poem was about a friend of his named Edward Thomas who thought a lot about how our decisions cannot be taken back and about how much those decisions impact our lives. Finally, you can simply say that the narrator is no one in particular -- just a random human being. I lean towards this idea because the ideas of the poem are universal -- they don't depend on who the speaker is.
As to audience, I think it is just a person thinking in his or her own mind. I do not think the speaker is addressing any other person. After all, the whole poem goes on in the speaker's head at that crossroad.
There is a special "universal" feeling about this poem that many poems reach for but do not quite achieve. As such, the poem itself stands as a metaphor for life. The author and audience, while subject to much interpretation, can certainly be viewed as one universal person speaking on behalf and to all other human beings. This is our situation. This is our road, our life. Some will choose to go the easy way, others will take a road less traveled. In describing it, it can sound trite. But, because it is done so artfully, Frost manages to risk sentimentality, to risk being trite, and emerges successfully with an iconic poem.
The poem, The Road Not Taken composed by Robert Frost provides a philosophical reflect imaging a process of making decisions which suffer from torques. Apparently, the poem talks about the status of the poet's journey, but a deep insight into the poem shows that it protrays the journey of the life itself. The poem is a dramatic lyric involving a single actor, the poet himself. It is akin to a soliloquy of an actor in a play. Here, in the poem, The Road Not Taken the poet is addressing his own mental differences which need a self-made clarification for selecting a particular life-style. besides, the readers are ofcourse passively addressed.