This paper has outlined the most important elements of CA use in transportation applications. Besides the standard CA rules of ``traffic on a link'', the important aspects are, that the dynamics unfolds on a graph instead of on flat space, and that the particles are intelligent. Both aspects make simulation packages considerably more complicated, the first since intersections need to be modeled; the second since the ``intelligence'' of the travelers (route choice, destination choice, activity generation, etc.) needs to be modeled. Finally, the limits of the CA technology were discussed. These limits exist in two directions: (1) The driving logic of the CA rules may not be realistic enough, and making it more realistic may be computationally as expensive as moving to coupled map lattices (discrete time, contiuous state space). (2) The available real world data may not be detailed enough to feed a realistic CA-based micro-simulation.
This paper and in particular the work on the simulation of ``all of Switzerland'' would not have been possible without the help of Kay Axhausen, Nurhan Cetin, Christian Gloor, Bryan Raney, Milenko Vrtic, Res Voellmy, and Marc Schmitt.