Toward Demonstrating Predictability of Bottleneck Activation on German Autobahns

Abstract

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.

Automated Analysis of Cumulative Flow and Speed Curves

“…Use of such curves in empirical traffic research dates to Cassidy and Windover (1); to date, the curves have been applied in two different ways. The first is to use rescaled cumulative flow curves from successive locations along a roadway (often referred to as N-curves) to study accumulation of vehicles in roadway segments (2)(3)(4)(5)(6)(7)(8). In this application rescaling consists of translating the curves in time by plotting them in moving time coordinates and (in most cases) rotating them so as to make changes in the flow rate (represented by the slope of the cumulative curve) more visible.…”

Extending Adaptive Cruise Control to Adaptive Driving Strategies

“…• Most traffic breakdowns are initiated at some sort of road inhomogeneities or infrastructure-based bottlenecks, such as on ramps, off ramps, and sections of road works (19)(20)(21) • An effective measure to avoid or delay traffic breakdowns is to homogenize the traffic flow.…”

Evaluation of N-Curve Methodology for Analysis of Complex Bottlenecks

“…Although the N-curve technique has proved to be quite powerful in past studies of bottlenecks and other flow phenomena (4)(5)(6)(7)(8)(9), it is vulnerable to the accumulation of errors resulting from biased counts (i.e., those that violate the vehicle conservation principle). Consequently, there may be situations in which its use is not appropriate.…”