Demand-depending Strategic Railway Network Evaluation
M Kettner and B Sewcyk, Institute of Transport, Railway Construction and Operation, DE
All railway companies face the complex task of using their resources efficiently. Thus, they have to optimise the planning of any measures concerning infrastructure and railway opera-tion. For this task, the Institute of Transport, Railway Construction and Operation (IVE) at the University of Hanover, Germany, has developed a strategic network planning and traffic evaluation model (NEMO: Network Evaluation MOdel). This simulation tool enables infra-structure managers to evaluate the effects of changes to the existing network. Furthermore, it is an instrument to estimate the efficiency of new transport services.
The model consists of several modules for projecting infrastructure, passenger traffic, and freight traffic. On the basis of train numbers determined by these modules, bottlenecks are identified and eliminated by help of a module for the network evaluation. The module evaluating economic efficiency calculates the costs and revenues that are to be expected when realising the simulated scenario.
The either given or planned railway network is projected by the means of an infrastructure graph that consists of nodes and links. Infrastructure attributes, influencing the services provided, expenses and revenues are assigned to the graph's components.
The module for projecting the passenger traffic provides a comparison of the services offered and the capacity demanded. Basis for the simulation are the restrictions imposed by the infra-structure and the current or planned passenger services. In an equilibrium process, offer is brought into line with demand.
This is done by the help of a modal-split model, which deter-mines the relation between railway and road traffic.
The module for projecting the freight traffic is based upon traffic volumes between different regions, the infrastructure and the operational strategies (production systems) of rail freight traffic. The freight volumes by region are assigned to the freight access points within a region. In order to connect the freight access points, an origin-destination-matrix is created. The whole amount of freight is then assigned to the respective production systems of the freight traffic. In cases where the quantity between two freight access points exceeds a certain amount, direct block trains are created. The remaining transport volume is transported by the single wagonload traffic. These wagons are rearranged in marshalling yards. The wagon volume is assigned to model trains which are defined at the network's links. For each of these links, the number of necessary model trains is then determined. Thus, the resulting use of the infrastructure by freight traffic can be derived. Empty stock wagons are taken into account by determining the shortage or surplus of freight wagons at the access points. This imbalance is levelled out by an optimised disposition of empty stock wagons. This is done by a System For Optimal Vehicle Disposition (DISPO++), also developed at the IVE and currently in use at several universities and railway companies like TU Berlin or Queensland Rail Australia.
The module for the evaluation of the network is based upon the results of the two modules projecting passenger and freight traffic. The calculated train numbers are combined to the total infrastructure load. Since capacity-caused bottlenecks only occur during certain times of day, the network load is examined for separate time slices. Within the time slices, bottlenecks are identified and dissolved by the use of suitable modifications to the operation program. While handling the bottleneck dissolutions, appropriateoperational measures are to be chosen in order to dissolve the detected bottlenecks. After the dissolution of all bottlenecks, services are supplied that can have effects on the modal-split of road and railway. If this is the case, the calculations of the modules passenger traffic, freight traffic and traffic assignment have to be repeated until an equilibrium of services offered and capacity demanded is achieved.
Subsequently, the module for the evaluation of economic efficiency calculates the arising costs and revenues on the basis of the computed transport supply and demand. On the one hand the model includes fixed cost assumptions for the infrastructure and the model trains. On the other hand, the revenues for the given transport services are predefined. A comparison of the total costs and the total revenues leads to the economic evaluation of the computed scenario. By these means, the economic benefit by planned measures concerning infrastructure and service can be estimated already before its realisation.
The described strategic network planning and traffic evaluation model NEMO is currently used by the Austrian Federal Railways (ÖBB) and Rail Cargo Austria (ÖBB GB GV). The future development concerns the integration of the software system RailSys, also developed at the IVE. RailSys is a detail-exact model for the accurate simulation of the railway operation procedure of any size networks. It will provide accurate running times and the minimum headway between trains. Thus, it enables dynamic scheduling based on the services supplied and will furthermore allow a detailed bottleneck dissolution choosing the appropriate train sequence.
Association for European Transport