Transport demand represents the essential basis in the design of public transport services. Information on this is accordingly a necessary prerequisite for the preparation of supply. In the following, a general approach is presented using the example of the European night train market, with which potentials can be derived despite little knowledge of the mobility needs of the market and demand matrices can be drawn up as a basis for economic calculations. By calculating a heuristic rule, the optimal path through a network in line planning is not exclusively a function of the edge evaluations but considers the node potentials determined this way. Transport demand represents the essential basis in the design of public transport services. Information on this is accordingly a necessary prerequisite for the preparation of supply. In the following, a general approach is presented with which potentials can be derived despite little knowledge of the mobility needs of the market. In the context of graph theory, the potential of nodes is evaluated and these are included downstream to the edge selection in form of a rucksack problem. By calculating a heuristic rule, the optimal path through a network in line planning is therefore not exclusively a function of the edge evaluations but considers the node potentials as well. Based on this demand matrices can be drawn up as a basis for economic calculations. Regarding the current debate on the expansion of night train services in Europe, this approach can be adapted to the conception of an overnight train. An overview of all night trains in Northern, Central and Western Europe in 2021 is provided for this purpose and the suitability of the approach is demonstrated using an example. It will be successful in setting up a route network from which passenger flows can be derived. However, possible adaptions that can be considered as second-best solutions are not taken into account and require further development of the approach.