In this paper, hybridization of a BB460000 locomotive is proposed integrating a reduced power diesel generator, batteries and ultracapacitors as storage elements. The power mission of the BB460000 locomotive is studied in order to analyze its ability to be hybridized and to identify the most critical mission. An energy management strategy based on a frequency sharing is proposed. It allows strongly decreasing the nominal power of the diesel generator. Then, through a power flow sizing model, the hybrid locomotive is sized with Ni–Cd batteries and ultracapacitors. The uselessness of ultracapacitors on energetic, geometrical, financial and lifetime plans is shown.