Question

Walking down the middle of the road .... Parts of speech of middle

Answer 1

The part of speech for middle is noun.

Answer 2

"Middle" here is an adjective, funnily enough.

This is due to the fact that "road" is a noun, which is being described by "middle".

"Of" is a possessive preposition

"Walking" is the action and hence is a verb

"Down" here is describing "middle" which is an adjective

Hence, "down" is an adverb.

Hope this helps!  :⊃