Vehicles with increasingly advanced automated capabilities are rapidly becoming a reality, and data are needed to understand the operation of the various types of these vehicles currently in use on public roads. This project is investigating real-world driver interaction with market-ready mixed-function automation (MFA) through a naturalistic driving study (NDS). The vehicles being used in this study have the capability to simultaneously activate automated lateral and longitudinal functions, allowing drivers to operate the vehicle with their hands off the steering wheel and feet off the pedals for several seconds, with the caveat that this capability is not explicitly stated or condoned by original equipment manufacturers (OEMs). All systems generate alerts to notify drivers to regain control of the vehicle. This study will observe and evaluate how drivers operate five different commercially available vehicles equipped with MFA. The study will recruit a total of 120 drivers from the Northern Virginia and Washington, DC metro area. Drivers will drive one of the study vehicles instead of their own for a period of four weeks. Study vehicles will be instrumented to capture vehicle data as well as audio and video. The data collected will be sampled and analyzed in order to assess drivers’ overall use of the systems and specific types of interactions—such as the sequence of events when regaining control and secondary task engagement. It is anticipated that interactions with the MFA features will be observed in operation in mixed traffic under a variety of roadway types, driving conditions, and speeds. At present, 47 drivers have completed their 4-week participation period, with an estimate of at least 56,400 miles driven. This project will support the identification and/or refinement of human factors best practices to encourage the safe operation of highly automated vehicles.