Hi Jackson,
"He" is in some location, possibly unable to find transportation. Actually, "frequency" in this context is usually applied to busses. One usually calls by telephone for a taxi cab, unless one is in the city at a busy time, and can "hail" a passing cab which is unoccupied. In a remote area late at night, if he's "lucky" enough to see a cab passing by, it will most likely be occupied.
The subjunctive seems to be optional these days in this sort of sentence.
Edit. Looking at the word "there," I suspect there's some context preceding this, in which he conceives a plan to walk to some other location, where he hopes to have better luck.
P.S. a suggestion on your question: a different word order, plus the verb "be" - "What could the context for the above sentence possibly be?"
Best regards, - A.