Open source mass transit trip planning applications provide real-time transit information for a local community. The application provides local users with an inexpensive and accurate way to predict when their bus will arrive at the bus stop. Researchers and instructors have used the One Bus Away application as an opportunity to form cross-disciplinary development teams similar to the ones that students will experience in professional development environments. The study shares the lessons learned, the guidelines developed, and the best practices for designing transit trip planning interfaces during two implementations. User testing revealed that online mapping applications must support both riders who are familiar with the city (i.e., resident riders), as well as riders who are only visiting (i.e., visiting riders). In both cases, riders must rapidly understand the interface icons and metaphors during significant cognitive stress, environmental stress, and anxiety about missing their bus.