Toward Demonstrating Predictability of Bottleneck Activation on German Autobahns

Traffic conditions were examined along 30 km (18.6 mi) of northbound Autobahn 5 near Frankfurt, Germany, with archived inductive loop detector data recorded at 1-min intervals. With a focus on the spatiotemporal evolution of traffic between freely flowing and queued conditions, it was possible to identify 15 bottleneck activations and to characterize reproducible features related to their formation, discharge, and dissipation. This was done by systematically probing the excess vehicle accumulation (spatial) and travel time (temporal) that arose between measurement locations. Bottlenecks became active in the vicinity of on- and off-ramps. The evolution of a steady shock of low flow, low velocity, and relatively short duration was traced over 16 km (10 mi). Its cause is not known definitively, but some indications of its formation were revealed. Once a bottleneck became active, its measured outflow was reproducible across multiple activations and multiple days. The analysis tools used were transformed curves of cumulative vehicle count and cumulative time mean velocity, with loop detector data in their most raw form. These cumulative curves provided the resolution necessary to reveal the spatial and temporal aspects of dynamic freeway traffic flow phenomena. With increasing availability of reliable freeway sensor data, it is important to continue the systematic empirical analysis of freeways in different countries with different geometric configurations. The results of this kind of research program will assist with all aspects of traffic flow modeling, operations, and control.