The transmission grid requires new upcoming electrical connections, resulting in limited capacity of the existing overhead lines. One of the possible solutions of the problem is to build the overhead lines and substations. Designing of overhead lines is associated with several considerable technical, environmental and economical problems. The paper deals with the concept of multi-objective optimization of the selection of the optimum transmission line route, including the choice of tower types, the coordinates of tower placement, tower geometry, conductor types and parameters, insulator types, damper types, earthing and lightning systems, span lengths. The optimization is organized in five stages. At the first and second stages, there is a search for a set of optimum solutions set as well as determination of the main impacting factors. The next two stages present two-objective optimization by using Pareto approach. At the last stage, which is described on the example of a case study, then probability of the occurrence constrain violation conditions is assessed. The cause and its prevention methods are identified. The presented approach is based on a real line design case with the main purpose to minimize the total invested capital and maximize the net present value. The results are reviewed in the paper.