- He is going up the mountain road.
- He is going up along the mountain road.
In 1, up is working as a preposition, while along is the preposition in the 2.
Do the both carry same meaning?
Prepositions are always used with verbs and adding a preposition to the verb may change the sentence meaning drastically, specially if the verb is a movement verb (go, walk, run...)
In the first sentence, you have the preposition up with the verb go, which gives the sentence a meaning of someone moving to the top of the mountain road.
In the second sentence, you have two prepositions modifying the same verb, you have up and along, which gives the reader the impression that someone is moving to the top of the mountain road and while moving along it.
John jumped into the portal
John jumped down into the portal
In the examples above, clearly down is not necessary since the main idea is going into the portal. However, it highlits the fact that the portal was somewhere under the ground, which requires John to jump downwards in order to be in it. Now, suppose that the portal is in front of John, then he can't jump down into it, instead he needs to jump forward into it.
Both sentences carry the same meaning.