DECLAIMERThis report was prepared as an account of work spotrsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or as~mes any legal Iiability or responsibility for the accuracy, ampleten-or usefulness of any information, apparatus, product, or process disdosed, or represents that its use would not infringe privateIy. Abstract. Large scale microscopic (i.e. vehicle-based) traffic simulations pose high demands on computational speed in at least two application areas: (i) real-time traffic forecasting, and (E) long-term planning applications (where repeated "looping" between the microsimulation and the simulated planning of individual person's behavior is necessary). As a rough number, a real-time simulation of an area such as Los Angeles (ca. 1 million travellers) will need a computational speed of much higher than 1 million aparticle" (= vehicle) updates per second. This paper reviews how this problem is approached in different projects and how these approaches are dependent both on the specific questions and on the prospective user community. The approaches reach from highly parallel and vectorizable, single-bit implementations on parallel supercomputers for Statistical Physics questions, via more realistic implementations on coupled workstations, to more complicated driving dynamics implemented again on parallel supercomputers.