There ought to be a word
for the way you know how to get some place
but don't remember the names of streets
The poem speaks of a number of things. For one, the very real phenomenon of knowing how to get around a place or from one place to another without necessarily knowing street names, exact distances, or any other details you could readily use to direct other people. It's just a route you've taken so often it's embedded in your cognition, your senses and muscles. You don't have to think about it, and if you do, the details that emerge will probably be meaningful only to you.
That's another thing about this poem - how ultimately personal life and its travels are. We can share our perceptions with others, but at a fundamental level we experience the world alone; no two people will perceive, experience, think about something the same way. We can always do our best to share though, invite people into our minds (as far as they can go).
Another beautiful excerpt:
then the road turns sharply uphill past a red barn
where a black dog jumps out to race you for a quarter mile
and finally recedes in the mirror like a disappointment
The dog offers enthusiasm, joy, and simple companionship; these are kept at the roadside, never embraced, as the journey unfolds.
the road winds vaguely past
houses people road signs
while time hums in your ear and you remember
the dream you left behind that morning
There's a shift from the outward senses and the external world (which, even if experienced differently, can still be acknowledged and experienced together) to the writer's inner world, to a dream that only the writer knows about and no one else can guess at. The traveler's at a place where really no one can follow her.
Now I'm going to go off on a neurology-related tangent:
The poem reminds me of an article I read a few months back on episodic vs. semantic memory. Episodic memory is the term used to describe our memory for autobiographical events, our personal narrative; semantic memory is for general knowledge (knowing the state capitals, or what a watch is used for, or the multiplication tables). The two kinds of memories can certainly overlap and be enmeshed, but there are also distinctions between them; these distinctions can be seen, for example, in people with certain kinds of neurological damage that predominantly affect one type of memory but not the other.
In one neurological study, a person with episodic memory amnesia was asked to describe his old neighborhood. He could remember major landmarks and broad, general spatial relations between different places. But it was all a brittle, bare sort of mental map, very sparse. Minor landmarks and details were absent. Associations, memories, the whole personal feel was gone; I don't think he would have had the experience of the person in Travel Directions, being able to describe a journey based on such personal recollections/associations rather than the most abstract generalities.
(Though I'm not sure how he well he would navigate those places on foot, and I forget if they gave him such a test. Episodic memory can also be distinct from motor memory; for instance, a person with episodic memory amnesia would not necessarily lose his ability to play the piano, so maybe he could walk around his old neighborhood in habitual accustomed routes.)