In recent years, driver drowsiness has been one of the major causes of road accidents and can lead to severe physical injuries, deaths and significant economic losses. Statistics indicate the need of a reliable driver drowsiness detection system which could alert the driver before a mishap happens. Researchers have attempted to determine driver drowsiness using the following measures: (1) vehicle-based measures; (2) behavioral measures and (3) physiological measures. A detailed review on these measures will provide insight on the present systems, issues associated with them and the enhancements that need to be done to make a robust system. In this paper, we review these three measures as to the sensors used and discuss the advantages and limitations of each. The various ways through which drowsiness has been experimentally manipulated is also discussed. We conclude that by designing a hybrid drowsiness detection system that combines non-intusive physiological measures with other measures one would accurately determine the drowsiness level of a driver. A number of road accidents might then be avoided if an alert is sent to a driver that is deemed drowsy.

In recent years, driver hypovigilance (drowsiness and inattentiveness) is one of the major causes for road accidents and it leads to severe traumas such as physical injuries, deaths, and economic losses. Several researchers have reported on driver drowsiness detection and only very few works have been reported on detecting the driver hypovigilance. The physiological signals and vision based approaches are mostly used for estimating the driver's hypovigilance. When the physical state of the driver is drowsy or inattentive, it is important to alert the driver through alerting methods to avoid the accidents. In this paper, we have reviewed various methods used to alert drivers and the issues involved in detecting the hypovigilance. There are many methods adopted for alerting the driver during hypovigilance such as alarms, visual effects, vibrations, etc. This present work discusses in detail about the different methods used for driver alertness system. The level of alertness is based on the hypovigilance level of the driver. The hypovigilance detection system should be designed in such a way to efficiently trigger the alert system only when the driver is in hypovigilance state.