Advanced Driver Assistance Systems (ADAS) such as Lane Keep Assist System (LKAS) offer drivers both convenience and safety benefits. However, assessing ADAS safety benefits can be challenging because crash reports typically include no information as to whether a system was active at the time of a crash. For example, LKAS systems are often disabled by drivers and may be unavailable to assist even when enabled, reducing the safety benefits of the system. However, the precise circumstances in which LKAS is unavailable remain not well known outside organizations directly involved in ADAS system design. This study seeks to make such information more broadly available, exploring the usage and effectiveness of ADAS, with an emphasis on LKAS, using in-vehicle message, accelerometer, and location data. In this study, data loggers were mounted in twelve vehicles owned or rented and driven by employee volunteers. Vehicle message data was decoded and standardized, with a focus on ADAS-related messages. Location data was merged with road feature and weather data. Decoded vehicle messages included fields identifying when the driver turned LKAS on and when the system was ready to assist the driver. Conditions in which the system was active or inactive are described, including two scenarios (concrete bridges and cloverleaf intersections) where the system repeatedly became inactive. [ABSTRACT FROM AUTHOR]