Why is the chicken crossing the road joke funny? According to modern psychology why is the answer to the joke "Why did the chicken cross the road?" "To get the the other side." Funny?

According to the relief theory, what are we relieved about?

Could it be that the question invokes a feeling of stress when we don't know the answer? Do we fear that we shall have to expend a lot of energy in trying to work out the solution? Is it stressful having a question put to us which we can't answer? (Just like starting a new job where we don't know what we're doing?)

Or does the stress come from the fear that we will look stupid for being unknowledgeable about the answer to the question?

Why are we then relieved by the answer? Is it because we are relieved that we don't have to expend new energy storing new information because we the information is already so obvious? (But this might not make sense as we do tend store jokes.) But we do not have to alter any of our existing information.

Or does the relief come from finding out that the questioner does not have superior knowledege to ourselves. And we laugh at how idiotic this person is. Like shadenfrauder. 

Or... is the laugh a submissive behaviour that we acknowledge that we have been fooled by a greater wit and intelligence?

What is the modern take on this?
I think, as you surmised, the joke isn't all that funny. I would consider the dynamics of the social interaction in which the joke was told as more important than the joke itself. 

Laughter is as much a social phenomenon as an involuntary reaction to something humorous. Duchenne laughter is even correlated with increased pain tolerance, in addition to feelings of well-being (https://doi.org/10.1098/rspb.2011.1373). People may laugh or otherwise respond positively if they are seeking social or personal approval.

But as an example of an infamous anti-joke, the chicken-road question "humor" is probably the relief of stress caused by the knowledge that the answer is trivial and thus we are obviated of the need to seek a more clever answer that would render this more of a riddle. The expectation is that the answer is something clever, interesting, or non-obvious, and so when the punchline is revealed, we are relieved and also fooled. The relief comes from the realization that it's not actually important what we said because the joke was a trick and our intellectual status was never on the line.

You may be interested in My Humorous Robot, a conference paper on human responses to an NAO robot telling jokes. The jokes range from actually funny to anti-jokes and human responses are statistically analyzed.

HRI '18 Companion of the 2018 ACM/IEEE International Conference on Human-Robot Interaction
Pages 193-194 
https://dl.acm.org/citation.cfm?id=3177015