Final answer:
The correct preposition for the provided sentence is 'in', making the sentence 'Parking the vehicle in the middle of the street is prohibited.' 'In' is the appropriate preposition when referring to being inside or within an area.
Step-by-step explanation:
The correct preposition to use in the sentence 'Parking the vehicle at the middle of the street is prohibited' is 'in'. The sentence should read, 'Parking the vehicle in the middle of the street is prohibited.' The preposition 'at' typically indicates a specific point or location, while 'in' is used to convey being inside or within an area. When talking about the general area of the middle of a street, 'in' is the appropriate preposition. This difference is important for clearly communicating the intended message and maintaining grammatical accuracy in English.