Answer:
Prepositional phrase: on the road
Type of phrase: Adverbial phrase
Step-by-step explanation:
A Prepositional phrase is simply a collection of words which has a modifier, a preposition and an object.
An Adverbial phrase is a type of phrase which performs the function of modifying a verb, adverb or adjective in a sentence by acting as an adverb.
Therefore, from the sentence, "Under-inflated tires drag on the road and reduce fuel efficiency", the prepositional phrase is "on the road" and it is an Adverbial phrase