Decision Support for Control Design of Rail Infrastructures

Designing control for rail infrastructures is a challenging task. Many aspects influence the system performance and have to be taken into account, such as physical layout of the network, vehicle types, expected passenger movements, control system characteristics and safety measures. Control designers have to test different combination of these aspects, by varying the configuration possibilities and analyze how the system will operate. Existing tools do not support the full assessment of control strategies before implementation. Normally, control strategies are tested in an isolated manner and control decisions are usually made based on employee’s experiences and on results of historical data analyses. Although these methods are of importance, they should not be the main basis for decisions. The disadvantage of data analyses is that they might lead to wrong decisions, if the analyzed data set is related to a part of the infrastructure where different control strategies were in use before. The employees’ expertise should be complemented with IT support, as the complexity of control design grows accordingly to the size of the infrastructure and the number of aspects that can vary. To address this problem, we propose a rail simulation library where rail control designers can evaluate the impact of different control strategies on the system through animation and statistics. This supports the choice of control strategies that will be more appropriate to the actual infrastructure. The design of our simulation library follows the concept of Next Generation Decision Support Systems to support users more effectively. In this paper, we describe a case study carried out in a tram company to test how this simulation library supports decision-making during control design process of rail infrastructures. 1. CHALLENGES IN DESIGNING CONTROL FOR RAIL INFRASTRUCTURES When designing control for rail infrastructures [20], control designers have to consider control strategies that will keep the performance of the rail system on an acceptable level. Performance is measured according to a list of key performance indicators, such as regularity and punctuality of rail vehicles, average of travel time and speed average per line. In this paper, the authors refer to control strategies as tactical strategies that will influence the way the rail system will be operated. They are mainly related to setting the control signaling system configuration and infrastructure capacity management. Examples are setting the speed limits for vehicles, choosing the location and the type of traffic lights, choosing the location of sensors, making timetables. Designing control strategies for rail infrastructure is a challenging task [20]. Information about various aspects of the infrastructure needs to be collected: data about the physical infrastructure, safety constraints and control signaling. Control designers combine all these information and they need to make sure control strategies do not violate constraints, such as safety measures, and that control strategies will provide a good system performance, especially when strategies are applied together with other control strategies. To illustrate practical examples of the complexities encountered in the task of designing control for rail infrastructures, we use a case study carried out at HTM Personenvervoer NV, a Dutch tram company (HTM). HTM is investing in extending its rail infrastructure and it will soon provide collective transport services to more distant regions. To serve these regions, HTM managers have decided to use Light Rail vehicles. Light rail vehicles are lighter than trains and they accelerate and brake as fast as trams. With this purpose, new tracks are being built and in some parts of the infrastructure they will join existing tracks and share these tracks with trams. We focused our case at the analysis of the impact of one of these track junctions and we chose an area where the traffic is very intense, close to the central station. Many tram lines pass through the central station and the addition of new tracks close to this area is expected to have a high impact on other tram lines. Figure 1 illustrates what the infrastructure looks like in a region surrounding the city center of The Hague and figure 2 provides a sketch of what the infrastructure will look like when the construction of the new tracks is finished. With the addition of new tracks, it was necessary to redesign the control signaling system for this area in order to accommodate the traffic of light rail vehicles without decreasing the performance of existing tram lines. 1 Source: http://www.htm.net, accessed on January, 10, 2006. SimTecT 2006 Refereed