In this paper, an improved model of the vertical risers of a transmission line is proposed and validated. The proposed improved model, which can be readily implemented in the frame of a classical transmission line formulation, provides accurate results at frequencies much higher than the upper frequency limit of the classical transmission line theory. For example, for the assessed line (with a height above the ground of 10 cm), the improved model is still fairly accurate at around 1 GHz, whereas the classical model starts to deviate from the accurate solution at around 150 MHz.