This dissertation describes an empirical study of how changing conditions propagate in freeway traffic. To this end, curves of cumulative vehicle arrival number versus time were constructed from counts made at neighboring loop detector stations. These curves were modified and examined in ways that facilitated the study of traffic flow features at a level of detail not previously possible.; In uncongested traffic, fluctuations in vehicle arrival rates propagated downstream. Between two detector stations, these fluctuations exhibited similar travel times, referred to as the free-flow travel time; this was observed for a number of station pairs. These observations implied that drivers chose to travel at nearly identical (average) speeds and/or to maintain their headways between measurement stations.; In congested traffic, measured vehicle arrival patterns at a downstream station were replicated (approximately) at upstream stations later in time. This indicates that changes in flow, along with the interfaces between the flow states, maintained their features as they propagated upstream. The interfaces, defined as disturbances, were observed to have narrow widths, meaning they passed over measurement stations in short periods of time. These observations implied that drivers adjusted their headways rapidly over each disturbance and that different collections of drivers responded similarly to each disturbance. This study also found that, between two stations, disturbances causing vehicle velocities to increase had statistically similar travel times and passed through statistically similar numbers of vehicles as those causing vehicle velocities to decrease; this was observed for a number of station pairs. Some features of the interface between uncongested and congested traffic, defined as a shock, are also described.; An understanding of these features is required to develop and/or to test theories of traffic flow which are needed for evaluating highway facilities. To this end, a description of how the observed traffic features can be modeled is contained herein. This description, which implies a triangular shaped flow-density curve, is consistent with Newell's (1993) "Simplified Theory of Kinematic Waves in Highway Traffic." A qualitative discussion of how well some other traffic flow models predict the observed traffic features is also contained herein.
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