This document provides security design guidance on three major transit system components - bus vehicles, rail vehicles, and transit infrastructure. It provides a resource for transit agency decision makers, members of design, construction and operations departments, security and law enforcement personnel and consultants and contractors, in developing an effective and affordable security strategy following the completion of a threat and vulnerability assessment and development of a comprehensive plan. Developed by the Federal Transit Administration in collaboration with transit industry public and private sector stakeholders, these design considerations provide actionable steps that transit agency staff can select from to create a security strategy.