Older drivers represent a high-risk population on the road, due to age-related declines in cognition and perception. The present research investigated whether an Older Driver Support System (ODSS) smartphone application would be useful. The research presented here was comprised of (1) focus groups, surveys, and interviews, (2) simulated driving with video playback, and (3) on-the-road field-testing. The methodology centered on iterative re-design of the ODSS interface based on feedback and behavior of older drivers. This iterative re-design approach was successful at making the ODSS interface more usable when considering System Usability Scale (SUS) scores. Furthermore, older drivers during the field test reported minimal mental effort expended when using the smartphone application and many significantly positive statements about the application. The field test resulted in several final recommendations for the ODSS application. A promising final takeaway was a universal design approach preferred by the older drivers, as they did not want to be singled out for special attention.