Increasingly, public transportation systems are equipped with Global Positioning Systems (GPS) connected to control centers through wireless networks. Controllers use this infrastructure to schedule and optimize operations and avoid organizational problems such as bunching. We have employed this existing infrastructure to compute highly personalized information and deliver it on PDAs and cell phones. In addition to guiding people using public transportation by showing them which bus they should take to reach specific destinations, we track their location to create spatial awareness to a community of users. An application of this technology, called Mobility Agents, has been created and tested for people with cognitive disabilities. About 7% of the U. S. population has a form of cognitive disability. Cognitive disabilities are limitations of the ability to perceive, recognize, understand, interpret, and respond to information. The ability to use public transportation can dramatically increase the independence of this population. The Mobility Agents system provides multimodal prompts to a traveler on handheld devices helping with the recognition of the "right" bus, for instance. At the same time, it communicates to a caregiver the location of the traveler and trip status. This article describes our findings at several levels. At a technical level, it outlines pragmatic issues including display issues, GPS reliability and networking latency arising from using handheld devices in the field. At a cognitive level, we describe the need to customize information to address different degrees and combinations of cognitive disabilities. At a user interface level, we describe the use of different mission status interface approaches ranging from 3D real-time visualizations to SMS and instant messaging-based text interfaces.