How should I proceed when a complicated question gets an excellent response to part of the question?

Question

The sole answer for Do lower speed limits reduce gasoline usage? fully addresses the core of my question and I would consider it pretty damn close to a complete answer even though it doesn't directly address the rest of the question. Is this a sign that:

• My question is too complicated
• The answer is not complete enough to accept
• ... ?

My instinct is to either upvote or accept but not both. The upvote would be for an excellent answer; the accept would be admitting that it is close enough. For some reason I hesitate doing both because I am still unsatisfied with regards to the full extent of what I wanted to know. I don't have a problem with this; I am still just trying to understand how to ask and answer questions here.

Answer 1

In this case, I would probably upvote but not accept. While it's a good answer, it doesn't fully answer what was asked in the title: do lower speed limits reduce gasoline usage?

After upvoting his answer, I strongly encourage you to leave a comment on the answer explaining why you did not accept the answer. With a bit of luck, the user will make the appropriate amount of research to completely answer your question (or someone else will, after seeing your comment).