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TRB 2003 Annual Meeting CD-ROM Paper revised from original submittal. Car-following models have been used in all microscopic traffic simulation models, for almost half a century, to describe the process of driver behavior while following each other in the traffic stream. However, previous experimental studies and models on car-following behavior have some important limitations, which make them inconsistent with real driving experiences. This study aims to investigate and disclose some important limitations of previous experimental studies and models on car-following behavior, and to provide some possible directions that might help improve the reality of previous car-following models. Data collection techniques are much better now than they were when much of the seminal data in this field was collected. With new high-fidelity data and better stochastic models, the realism of microscopic traffic simulators could be improved greatly