This paper presents findings of an ongoing empirical study focusing on identification and examination of several recurring freeway bottlenecks. It integrates the fusion of several traffic management and driver infor- mation data sources along an 18-km (11.2-mi) section of Autobahn 9 near Munich, Germany. These combined data sources further understanding of traffic dynamics and driver behavior before, during, and after bottle- neck activation. The primary focus of this paper has been the investiga- tion of variable speed limit and traveler information systems provided by means of overhead dynamic message signs so as to improve understand- ing of how these systems affect driver behavior and bottleneck formation and location. Toward that end, speed limit and information messages have been compared with actual traffic dynamics on the segment of Auto- bahn 9, and the analysis has found a strong correlation. It has been found that when drivers were warned of approaching congested conditions, the speed limit was reduced before bottleneck activation as a means of man- aging dense traffic. The system reduced the speed limit to control dense but still flowing traffic, and traffic continued to flow during congested periods at speeds between 30 and 40 km/h (19 and 25 mph). A comparison of sampled measurements of flow and speed with fundamental diagrams of speed–flow and flow–density indicated that speed limits were reduced. These findings will be connected to a before-and-after comparison of the system to be done to determine benefits and effects of such a system. The objective of this paper is to compare the variable speed limit (VSL) and traveler information presented to drivers via overhead variable message signs with actual traffic conditions as determined by detailed analysis of historical inductive loop detector data extracted from a segment of German Autobahn 9 (A9) near Munich, Germany. Freeway bottlenecks are important elements of a free- way system; therefore it is important to understand their unique characteristics, in particular their causation, location, and dissipa- tion. An active freeway bottleneck will be defined as a point on a freeway cross section upstream of which is queued traffic and downstream of which are unrestricted conditions, consistent with the definition provided by Daganzo (1). To emphasize the impor- tance of the careful diagnosis of the causation and dissipation of bottlenecks, this analysis includes the integration of variable speed limit and traveler information data to gain important information about the dynamics of traffic flow and physical freeway infra- structure before, during, and after the activation of a bottleneck near busy freeway on- and off-ramps. The analysis techniques used in this study include transformed curves of cumulative vehicle count and time-averaged speed versus time. These curves provided the resolution necessary to carefully and systematically diagnose bottleneck activation in both the spatial and temporal dimensions. Tutorials providing detailed descriptions of the procedures used to construct these transformed curves are shown in several references (2–5). Further, this paper builds on previous research conducted at this site, which includes a detailed examination of bottleneck activation and possible triggers (6, 7 ). In Europe, VSL systems are applied in an effort to reduce vehicu- lar crashes, postpone or prevent congestion, eliminate large speed dif- ferentials, dampen shocks, and harmonize flow during peak periods. The literature has indicated that the use of variable speed limits in Ger- many has decreased crash rates by as much as 20% (8). Currently, this section of A9 uses a series of algorithms to determine the most appro- priate speed limit on the basis of three control strategies. These are incident detection, harmonization, and weather detection. Harmo- nization refers to the control of dense but still flowing traffic and is used to postpone or prevent breakdown of the facility. To date, no sys- tem such as this has been implemented in the United States; therefore this paper hopes to ignite research on the subject by means of deter- mining whether deployment on U.S. freeways should be considered. As anticipated, this analysis has found that there is a correlation between the variable speed limit and driver information system and the actual traffic dynamics. On the basis of sampled observa- tions compared with the fundamental diagrams of speed–flow and flow–density, it was found that drivers were informed in advance of congested conditions and that speeds were reduced. Although speeds did decrease notably on bottleneck activation, traffic remained flow- ing; this may be attributable to the system’s effectiveness. Further analysis is scheduled to be conducted in the future to determine the effects of the system and its benefits. This paper will first introduce the data sources and methodology used followed by a discussion of actual traffic dynamics as deter- mined from detector data. Concluding sections compare the dynam- ics of the variable speed limit and driver information system with actual traffic dynamics to determine the correlation between them. DATA Fixed Sensor Data The study site, as shown in Figure 1a, is an 18-km (11.2-mi) sec- tion of southbound A9 located near Munich, Germany. The freeway Dynamics of Variable Speed Limit System Surrounding Bottleneck on German Autobahn Robert L. Bertini, Steven Boice, and Klaus Bogenberger R. L. Bertini and S. Boice, Department of Civil and Environmental Engineering, Port- land State University, P.O. Box 751, Portland, OR 97207-0751. K. Bogenberger, Science and Traffic Policy, Traffic Technology, BMW Group, 80788 Munich, Germany. 149 Transportation Research Record: Journal of the Transportation Research Board, No. 1978, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 149–159.