Drowsiness among commercial vehicle drivers has been identified as the number one safety concern of commercial fleets at trucking summit meetings. Over the past 10 years, the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) and its research partners have sought to quantify the loss of alertness among commercial vehicle drivers. This work led to the development of the world’s first unobtrusive and valid sensor of loss of alertness, and has been the benchmark for continuing international study. Replicated experiments have shown that the most valid measure of loss of alertness among drivers is the percentage of eyelid closure over the pupil over time (Perclos). Formerly pioneered by Dr. Walter Wierwille at the Virginia Polytechnical Institute and State University, using a manual observation technique[6], Perclos is now monitored in real time using machine vision technology in the vehicle. In order to estimate the highway safety benefit based on the effectiveness of the system, a Field Operational Test (FOT) is underway with long haul and express (i.e., overnight) fleet operations. This paper discusses the field test methodology, as well as the questions each analysis seeks to answer. A summary of the status of the project, the results to date, and a vision of future work for the deployment of this technology will be provided.