ABSTRACT: Traffic was studied on a thirty kilometer section of freeway north of Frankfurt Am Main, Germany using archived loop detector data. The spatial-temporal characteristics of over eighty bottleneck activations were diagnosed with six days of data. The analysis tools used were curves of cumulative vehicle count and time mean speed versus time. These curves were constructed using data from neighboring freeway loop detectors and were transformed in order to provide the measurement resolution necessary to observe the transitions between freely-flowing and queued conditions and to identify important traffic features.The bottlenecks' locations, pre-queue flows, and mean discharge flows across all lanes and on a lane by lane basis were found to be reproducible from day to day. Further, it is shown that the bottlenecks' mean discharge flow was about 3-5% lower than the mean prevailing flow prior to queue formation when freely flow conditions preceded the activation. Changes in key traffic parameters leading to the formation and dissolution of diverge and merge bottlenecks were investigated and were found to reproducible from day to day. The bottleneck formation triggers for diverge bottleneck activations preceded by freely flowing traffic included high flows across all lanes and high, truck dominated, flows in the right lane just upstream of the bottleneck location. For merge bottleneck activations preceded by freely flowing traffic, reproducible triggers included net lane changing to the left and increases in unmetered on-ramp flow of approximately 25%. Upon bottleneck activation, flow reductions occurring sequentially in time and space marked the passage of backward-moving shocks. Mean shock velocities were in the range of -18 km/h as they traveled upstream from the bottleneck locations. During periods of bottleneck activation, oscillations arose in the upstream congested traffic and propagated upstream at nearly constant speeds. The effects of some bottleneck activations in this study traveled upstream over 20 km, passing through several major interchanges. his research represents an important step towards a greater understanding of how and why freeways bottlenecks arise and some of their characteristics. Together with future empirical studies, this will lead to the development of improved traffic flow theories and freeway management techniques.

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