What is the allegory and what are the metaphors in "Stopping by Woods on a Snowy Evening?"

I'm not sure I would call Frost's "Stopping by Woods on a
Snowy Evening" allegorical in any sense.  One might say it's symbolic or that it
involves an extended metaphor, but I don't see it as an
allegory.

If the poem is symbolic or involves an extended
metaphor, it is in the sense that the absent land owner, separated from nature,
symbolizes humans who are separated from nature and don't realize what they're missing. 
Connected to this interpretation is the opposition of the man-made (such as the barn),
with the natural (the snow and woods).  The speaker/character, too, though he
appreciates the natural, cannot stay to admire it because of human
responsibilities. 

The poem may also close with a
metaphor:

And
miles to go before I sleep,

And miles to go before I
sleep.

Some commentators
suggest this is a metaphor for death.  In this interpretation, though the speaker longs
for the peace of death (sleep), he chooses to fulfill his responsibilities and promises,
rather than to seek what he wishes.