Driver support systems employ behavioral modification functions to assist drivers in adopting safer driving behaviors. This study utilized a smartphone-based driver support system, RoadCoach, that provided real-time, in-vehicle feedback to older adult drivers about detected risky driving behaviors (e.g., speeding, running stop signs, erratic vehicle maneuvering). The application also provided drivers with roadway information such as the current posted speed limit, upcoming changes to the speed limit, and sharp curves in the roadway ahead. The study evaluated the efficacy of in-vehicle feedback on reducing risky driving behaviors as well as self-assessment of driving ability among senior drivers. Driving behavior data were collected from groups in Minnesota, MN (N=14) and Wichita, KS (N=14) as they engaged in normal, everyday driving for twelve weeks. For the first three weeks of the study, baseline measurements of driver behavior were collected, followed by six weeks of in-vehicle feedback from RoadCoach, and finally, three weeks of no feedback. The results indicated an overall benefit of the presence of RoadCoach in significantly reducing speeding propensity, hard braking, and failure to properly slow or stop for stop signs. Additionally, there was a significant improvement in driver self-monitoring for speeding behavior and significant decreases in perceived mind wandering and perceived driving ability. The driver support system was also rated quite low in mental and visual demand. The outcomes of this study suggest that applications that provide older adult drivers with in-vehicle feedback are useful at reducing risky driving behaviors associated with an increased crash-risk, as well as improving self-assessments of driving ability.