Dialogue is not a characteristic of functional text because

Functional texts have the aim to explain something - usually, they can be found in the form of user manuals and such. Having this in mind, it would be very difficult to understand what is written if the whole functional text was written in dialogues. Dialogues are useful in spoken language, as well as in plays, and literature that isn't functional. 

Answer shorter following distance, increased speed, erratic lane changes,the answer would be all the above;