An autonomous vehicle (AV) implements a notification system that provides notifications to user devices in nearby vehicles to alert drivers of the nearby vehicles of the AV's planned behavior. The notifications are delivered wirelessly and output by the user device to the drivers. The planned behaviors of the AV may not be conveyed by existing mechanisms, such as turning signals or hazard lights. The AV or the receiving user device may determine when an AV's planned behavior may impact a particular driver, and provide relevant notifications to the driver.