This paper outlines design ideas from a project dealing with different interaction concepts for the design of a computer based navigation system for truck drivers. The incentive for thinking about interaction concepts is that programming of navigation systems often occurs while driving, since that is when the support is needed. We have been working with ethnographical studies of truck drivers driving both over short and long distances. There has been quite a lot of work done in the field of cars and navigation, in this paper however the main theme is not navigation in cars as such, but the truck environment as an example of a high-demanding room for work activities. This lead to a design situation where the artifact and the activity has to go together, the artifact has to ‘melt-in’ to the work practice. We discuss how the design of computational power can melt-in to the work-practice without demanding too much of the attention needed for driving the truck safely.