In this paper we analyse the correlation of a number of interpersonal features of language with success or failure of dialogues between humans and intelligent wheelchairs and peculiarities of the situation. We show that interpersonal communication as it is known from human-human dialogues holds as well for human-wheelchair interaction. We show how changes in politeness, gesture and usage of vocatives can be used to detect communication failure, how vocative and human roles convey information about the relative placement of the wheelchair with respect to the human, and how different strategies can be combined throughout interaction for identifying destinations.