The thesis discusses the planning of new and optimization of the existing lines of public transport. The first part provides a general historical context of the development of public transport and the development of public transport in Ljubljana. This is followed by the main guidelines, which are appropriate and necessary to consider when planning new lines. Various concepts of planning and their main features are presented. The second part features the analysis of the current state of the lines of public transport in Ljubljana and lists the main shortcomings of the existing system. Depending on the identified shortcomings and based on theoretical principles and guidelines, two new lines are presented, as well as one line with optimized and changed course in relation to the current condition. For new courses the results of the simulation are given, which was made using the software PTV VISUM. The last part of the thesis provides the evaluation of the results of simulations and gives an assessment of the relevance and adequacy of the proposed solutions.