Network Evaluation Model NEMO

Transcription

1 Network Evaluation Model NEMO Bernd Sewcyk, Michael Kettner Institute of Transport, Railway Construction and Operation (IVE), University of Hanover, Germany Abstract All railway companies face the complex task of using their resources efficiently. The customers ask for a combination of high quality and low price of the transport service. In order to cope with this challenge, the companies have to optimise the planning of any measures concerning infrastructure and railway operation. For this task, the Institute for Transportation, Railway Construction and Operation (IVE) at the University of Hanover, Germany, has developed a strategic network planning and traffic evaluation model. This new simulation tool enables infrastructure managers to evaluate the effects of changing the existing network. Furthermore, it is an instrument to estimate the success of new transport services, which is a very important information for railway operators. Introduction Variations of transport offers always also result in a change of a demand for transport. New products and changed operation programs influence the demand as well as changes to the network's structure. Therefore, an optimization of investment- and network-planning for railways demands a dynamical evaluation technique that considers these interactions. Using the planning model developed at the IVE, the network load is determined by taking into account the bases of projections for passenger and freight traffic. In an equilibrium process, a balance for transport offer and demand is found. The model evaluates both the costs and earnings, that result from the provided traffic services. The status quo is used as a reference case in order to calibrate the model. The calculations' results are of great importance for the operators as well as the infrastructure managers, because the success of investments can be estimated in advance. The model consists of single modules for projecting infrastructure, passenger traffic and freight traffic. On the basis of train numbers determined by these modules, the bottle-necks are identified and eliminated by a module for the traffic assignment. The evaluation model for the economic efficiency calculates the costs and earnings that are to be expected for a realization of the simulated scenario. Program modules

2 Survey of the Program Modules Module infrastructure The either given or planned railway network is projected by the means of an infrastructure graph that consists of nodes and edges. All entry points of the passenger and freight traffic, as well as all branchings or junctions within the network are represented by a node. The links in between the nodes are represented by edges. Attributes are assigned to the graph's components. For projecting operational processes for example, the number of tracks existing in a node is of great importance. The edges are being occupied by different model trains that have different running times and stops, depending on the type of train (passenger, freight) and on physical characteristics, (length, weight, traction). In order to evaluate the economic efficiency of the whole system, all nodes and edges are supplied with the referring model trains and expenses. The possible earnings are also being added. Railway network graph Module passenger traffic The module for projecting the passenger traffic provides a comparison of the traffic offered and demanded. Basis for the simulation are the restrictions given by the infrastructure and the current or planned offer for passenger traffic. In an equilibrium process, offer and demand are co-ordinated until they are balanced. The whole process consists of the following steps: Traffic volume In a first step, the whole traffic with origin in or destination to a region is determined, not regarding the means of transport. Traffic relations The created traffic within a region is divided considering the different destination regions and is assigned to the individual entry points. At the end of the process, an origin-destination-matrix between the passenger traffic s entry points is computed. Route search The passenger quantity in between the entry points is assigned to the model trains at the network's edges. The route search follows the criterions of shortest time and lowest costs.

3 Train composition With the help of the results of the route search, the number of model trains on each network edge can be determined. When doing so, the wanted capacity of the trains can also be taken into account. Therefore, a real network load is determined. Offer comparison The output of the train composition leads to a calculated train offer which is compared to the original offer. Computation cycle of demand and offer The determination of the traffic volume is made in advance of the first simulation and must be seen as a fixed input. All remaining steps are repeatedly carried out as a cycle: If the new offer shows changes, these changes influence the demands. This effect is evaluated by the help of the modal-split model, which determines the relation between railway and road traffic. Of prime importance by choosing the means of transport are the time of travel and the costs, which are calculated by the module passenger traffic. The whole traffic is subdivided into the areas occupation, education, business, leisure time and shopping. This subdivision is necessary because costs and time of travel are evaluated differently, and thus have no equal effect on the modal-split. Module freight traffic The module for projecting the freight traffic is based upon the details of the traffic's quantity in between different regions. Information about the infrastructure and the production system within the freight traffic on rail is also necessary. The calculations within the module consist of four steps: Traffic volume In each examined region, the originating freight that is transported by rail is calculated. These amounts are assigned to the entry points within a region. In order to connect the entry points, a origin-destination-matrix is created. Production systems of freight traffic The whole amount of freight is assigned to the production systems of the freight traffic. In case the quantity in between two entry points exceeds a certain amount, block trains are created that go directly. The remaining transport volume is worked off by the single-wagon-traffic. If so, the wagons are rearranged in shunting yards. Route search The wagon volume is assigned to the model trains which are defined at the network's edges. All production systems possess their own specific model trains. In the single-wagon-traffic, the marginal condition is applied that the wagons

4 have to go through a chain of shunting yards. For each wagon, the model computes the fastest and least expensive route within the network. Train composition For each of the network's edges, the number of necessary model trains is determined. Thus, the resulting load of the infrastructure by the freight traffic can be derived. In contrast to the projection of the passenger traffic, a modal-split is not calculated for the freight traffic. However, the transport quantity determined at the beginning can be reduced, if an in advance defined transport time is exceeded. Empty stock wagons are taken into account by determining the shortage or surplus of freight wagons at the entry points. This imbalance is levelled out by an optimised disposition of empty stock wagons. Therefore, an origindestination-matrix is developed, that has to be added to the referring matrix of the loaded wagons. Module traffic assignment The module traffic assignment is based upon the results of the two models describing the passenger and freight traffic. Those calculated train numbers are combined to the total infrastructure load. Time slices Because capacity-caused bottle-necks only occur during certain times of day, the network load is examined for seperated time slices. Within the time slices, bottle-necks are identified and dissolved by the use of suitable modifications to the operation programm. The complete period of time for a day is subdivided into four to eight time slices, so that bottlenecks can be adequately determined. By considering the whole day as only one time slice, bottle-necks could only be detected unsatisfactory. Bottle-neck identification The infrastructure elements (nodes, edges) are examined, taking into account whether their capacity is exceeded because of the calculated train numbers. If the computed trains cannot pass a route section within the concerning time slice without being delayed by other trains, there is a bottle-neck. Process of computation Bottle-neck dissolution While handling the bottle-neck dissolutions, appropriate measures are to be chosen in order to dissolve the detected bottle-necks. The module traffic assignment suggests various solutions. One possibility is to pick an alternative route for those trains that are not bound to certain stops. Block trains, for example, in between far away stops, could be considered for this solution. However, bottle-necks can also be dissolved by changing train speeds or modifying the infrastructure. The decision has to be made by the person using the module.

5 After the dissolution of all bottle-necks within the infrastructure, a traffic offer is 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 offer and demand is achieved. Module economic efficiency The module for evaluating the economic efficiency is based upon the results of the preceding calculation steps. On the basis of the computed train offer, the demand and the load of the infrastructure as well as all arising costs and earnings are calculated. On the one hand the model includes fixed cost suggestions for the infrastructure and the model trains. On the other hand, the earnings for the given transport services are predefined. A comparison of the total costs and the total earnings 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. Conclusions The strategic network planning and traffic evaluation model developed at the IVE supports the computer-aided simulation of scenarios in the areas infrastructure and service. The software system can be applied by all railway companies operating on sufficiently large track networks. Currently, the whole system is adapted for applications at the Austrian Federal Railway (Österreichische Bundesbahn ÖBB) The results are used by the ÖBB for evaluating changes to the infrastructure, because it is taken into consideration to build or extend railway routes.