The paper describes an approach to specifically tailored user interface design, to adapt the user interface to the specific needs of mobility impaired travellers. Given a user has some interaction impairments or s/he is in a situation that causes an interaction impairment (i.e. noisy environment has the same consequences as hearing impairment), another modality is to be used or adapted to compensate this impairment. As sound has other interaction characteristics than graphical user interface elements (e.g. information can not be presented in parallel, but sequentially), rules for substituting some modalities through others are described.