Several phases of a project seeking to improve the design of wood transmission line structures are presented. Improved information for wood pole strength includes a compilation of results from previous pole tests of new fairly short poles. Strength and stiffness values from a pilot study of transmission-size poles and poles removed from service are also presented. These test show that pole strength is significantly reduced by exposure to typical service conditions. In addition, limited tests of new transmission-size poles show results similar to those of previous tests of new short poles. A load and resistance factor design format with design factors based on reliability concepts is advocated as a practical method to improve design of transmission line structures by achieving a better balance of reliability and economy. The proposed utility use of equations for load and resistance factors containing design quantity variabilities and reliability index values allows the consideration of special conditions and encourages gathering of local data. An illustration of the reliability-based design method is also included.