Traction power systems experience some of the most extreme variations in local power loads as compared to most other large scale electric power supply networks. These variations create challenges in the construction of reliable electric power delivery systems and in the performance of the rolling stock dependent on power supplied by the system. Energy storage offers a solution by smoothing out these power variations, absorbing energy as system voltage rises, and delivering energy as voltage drops. This guide will aid engineers in identifying where these solutions can provide the greatest benefits, designing solutions with the greatest impact, and quantifying the costs and benefits of deploying new solutions. With the rapid evolution of advanced power electronics, control methods and storage technologies available, combined with the wide range of applications, it is not possible, nor desirable, to include specific design requirements which might limit or preclude new ideas and concepts from being developed. From a systems perspective, the goal of this guide is to provide an overview of the following: Common terminology used to describe performance; Common applications and technologies; Common equipment topologies; Specification of energy storage systems; Economic considerations and cost-benefit analysis; Modeling and simulation; Performance and functional considerations; Interoperability considerations; Tools and methods to verify safety; Installation and integration considerations; Tools and methods to measure and verify system performance