Public transportation systems are among the most ubiquitous and complex large-scale systems found in modern society. For those unable to drive such as people with cognitive disabilities, these systems are essential gateways for participation in community activities, socialization, and independence. To understand the magnitude and scope of this national problem, we highlight deficiencies identified in an international study by the Transportation Research Board of the National Research Council and present specific cognitive barriers identified in empirical studies of transportation systems in several U.S. cities.An interdisciplinary team of HCI researchers, urban transportation planners, commercial technologists, and assistive care specialists are now collaborating on the Mobility-for-All project to create architectures and prototypes that support those with cognitive disabilities and their caregivers. We have grounded our research and design efforts using a distributed cognition framework. We have derived requirements for our designs by analyzing “how things are” for individuals with cognitive disabilities who learn and use public transportation systems. We present a socio-technical architecture that has three components: a) a personal travel assistant that uses real-time Global Positioning Systems data from the bus fleet to deliver just-in-time prompts; b) a mobile prompting client and a prompting script configuration tool for caregivers; and c) a monitoring system that collects real-time task status from the mobile client and alerts the support community of potential problems. We then describe a phased community-centered assessment approach that begins at the design stage and continues to be integrated throughout the project.This research has broad implications for designing more human-centered transportation systems that are universally accessible for other disenfranchised communities such as the elderly or nonnative speaker. This project presents an “in-the-world” research opportunity that challenges our understanding about mobile human computer interactions with ubiquitous, context-aware computing architectures in noisy, uncontrolled environments; personalization and user modeling techniques; and the design of universally accessible interfaces for complex systems through participatory design processes.This article provides both a near-term vision and an architecture for transportation systems that are socially inclusive, technologically appealing, and easier for everyone to use.