A survey on drowsiness detection techniques^?

There are 1.24 million traffic accidents every year with 2.4% caused by drowsy drivers. In that context, several methods for drowsiness detection have been developed. Nevertheless, despite the huge amount of researches, the several devices on markets, and car systems; it is not clear which method is the most appropriate, what sensors are the most useful and least intrusive. This study, shows a systematic literature review of the most recently and relevant methods.