This paper deals with a concept of the stochastic optimization methodology of power line design, which allows optimize transmission network planning (TNP). The paper presents a comparison of both applied methods for the best line design alternative selection – deterministic economic intervals (EI) method and stochastic approach based (SAB) method taking into account market conditions. Both methods are utilized for overhead power line (OHL) design, including the choice of main line elements such as tower height, type and coordinates, conductor type and cross-section, line fittings etc. Moreover a use of High Temperature Low Sag (HTLS) conductors – a part of the advanced technology, were evaluated together with traditional type conductors. The optimization problem is formulated as minimization of the total annual operation and construction costs. The proposed methodology is tested in the developed tool, which is realized in MATLAB software by using Monte Carlo (MC) method and in overhead power line design program - PLS-CADD. Two basic case studies for verification the proposed power line planning solution are presented in a paper.