Microscopic Simulation With Aimsun For the Assessment of Real-time Traffic Management Strategies in Tunnels
J Barceló, Polytechnic University of Catalonia; J Casas, J Ferrer, Transport Simulation Systems, ES
The occurrence of very severe accidents in the Mont Blanc and the Saint Gothard tunnels in the Alps, has raised a big concern in Europe on the safety conditions in long mountain tunnels, easy to understand taking into account how many tunnels there are in the European mountains, most of them built a long time ago, consisting only on a two way carriage way, with one lane on each direction. These tunnels were not designed to support the current traffic flows that the ever raising demand generates, namely with respect to freight transport in tunnels crossing national borders, implying that a significant percentage of the traffic is composed of heavy trucks, some of them carrying hazardous goods and raising significantly the risk level. Most of these concerns also apply to long urban tunnels in the peripheral ring roads of large metropolitan areas.
These concerns have consequently lead the authorities to adopt measures to improve the safety in the existing tunnels as well as to modify accordingly the safety related aspects in the design of the new tunnels. In both cases specific traffic management policies play a relevant role. Microscopic traffic simulation can be applied to analyze traffic conditions in tunnels and to analyze the expected performance of traffic management policies designed to manage the safety in tunnels. This paper presents and discusses two cases of use of microscopic simulation for these purposes: the testing of a preventive policy in an old tunnel in the Pyrenees, and the assistance in the design of a new tunnel in Italy. For the first case, taking into account that not always is possible to build new infrastructures (i.e. opening a new tunnel) various alternatives have been proposed, either aimed at reducing the number of accidents through preventive safety measures, or active, based on strict control policies implemented with hardware technology, as in the case of specific devices for tracking heavy vehicles and force them to keep safety distances. Among the preventive one of the most simple but possibly effective management policies is trying to avoid that platoons of trucks traveling in opposite irections cross the tunnel at the same time, in order to avoid frontal and rear collisions
The proposed Traffic Management System for the Vielha 5.5 Km long tunnel in the Pyrenees between France and Spain built in 1949, was conceived in such a way that, further than improving the monitoring and surveillance of the traffic in the tunnel, avoids platoons of trucks traveling in opposite directions through the tunnel at the same time, becoming in that way a preventive policy that contributes to achieve the safety objectives. The reason for thinking in terms of platoons or groups of heavy vehicles instead of individual heavy vehicles is to increase the efficiency of the system in terms of level of service. Several alternative control and management strategies have been proposed to achieve these objectives. In essence the conceptual approach can be summarized as follows: the heavy vehicles approaching the tunnel are identified, assuming that the suitable detection stations are available upstream from the North and South Accesses to the tunnel. When a heavy vehicle is detected, if there is already another heavy vehicle traveling in the opposite direction in the tunnel, a Variable Message Sign panel displays a message asking the heavy vehicle to leave the road and head towards a waiting area standing before the tunnel (One before the South Access and two before the North Access). In this way: Heavy vehicles traveling north will be retained in the waiting area until all heavy vehicles traveling south have left the tunnel Then the traffic lights will stop the light vehicles traveling north and will open the pass to the platoon of heavy vehicles retained in the waiting area , at the same time heavy vehicles traveling south will be forced to wait in the waiting areas of the north access. Once the last heavy vehicle traveling north has left the tunnel the symmetric operation will begin for heavy vehicles traveling south waiting in the north access buffers. From a technical point of view the implementation of this approach consists on three main components:
1. The combined management of the two buffers before the North Access.
2. The combined management of the Variable Message Panels to reroute the heavy vehicles to the waiting areas
3. Management of the traffic lights to alternate the pass of the platoons
Three alternative control logics were proposed to manage the traffic lights:
1. A pre-timed control
2. A full adaptive control, and
3. A semi-adaptive control
From a methodological point of view microscopic simulation was chosen as the methodological approach best suited to achieve the comparison between the different scenarios of a future traffic system not yet implemented. The first case reported in this paper corresponds to the AIMSUN simulation study, conducted on behalf of the Catalan authorities, to identify the best one of those alternatives. The second case reports the microscopic simulation study conducted with AIMSUN for the analysis of the safety conditions of the Italian A1 motorway ?Bologna-Firenze? reconfiguration project, called ?Variante di Valico?, to evaluate the ITS devices that will monitor and manage traffic in the new 8 km long main tunnel, called ?Galleria di Base?, included in the project. The study gave interesting results in terms of effects on traffic management of the different ITS systems analyzed and suggested possible follow-up for identifying safety indicators to be provided by microsimulation techniques.
Association for European Transport