Acknowledgments

We thank A. Bachem, R. Schrader and C. Barrett for supporting MR's work as part of the traffic simulation efforts in Cologne (``Verkehrsverbund Verkehrsimulation und Umweltwirkungen NRW'') and Los Alamos (TRANSIMS). Computing time on the SGI-1 Challenger of the Regionales Rechenzentrum Köln and on the workstation cluster at TSA-DO/SA is gratefully acknowledged. The work of MR was supported in part by the ``Graduiertenkolleg Scientific Computing Köln''. Part of this work was performed at Los Alamos National Laboratory, which is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36 (LA-UR 98-2250).