Project Description

Recommendations for lighting systems in transportation applications are exclusively based upon visual considerations mainly because research efforts in the area of transportation has been focused on optimizing lighting systems for visibility. However, it is important to consider that light incident on the retina can also affect alertness as well as sleep quality and timing through the circadian system, a separate neural pathway in the brain. More specifically and relevant to transportation applications, light can have a direct, but heretofore, unspecified, non-visual impact on driver performance at night.

Circadian body rhythms (e.g., sleep-wake) repeat every 24 hours. These rhythms are regulated by an “internal clock” and the light/dark cycle (typically daylight and darkness) is the major synchronizer of the internal clock to the 24-hour day. Humans are genetically programmed to be awake during daylight and asleep at night but, of course, electric lighting technologies enable us to become asynchronous with the light-dark cycle. This asynchrony can negatively impact performance and alertness of drivers at night, thus leading directly to reductions in traffic safety, quite separate from reduced visibility at night. According to the Federal Motor Carrier Safety Administration's Large Truck Crash Profile: The 1998 National Picture, in about 1.5% of crashes involving large trucks, police reported that drivers appeared to be fatigued or very tired. More than 7% of single-vehicle fatal truck accidents were reported as having driver drowsiness or sleeping as a related factor, and these two statistics probably underestimates the problem. According to the 1990 World Almanac, each accident involving a fatality or very serious injury results in a cost of nearly $1.5 million, simply accounting for wage losses, medical expenses and insurance administration. Light applied during the nighttime has been shown in a variety of studies to increase alertness and reduce sleepiness as measured by brain activities and subjective scales. Therefore, light is an unexplored tool to increase driver safety at night.

The proposed working paper will review the research literature in circadian photobiology, lighting characteristics impacting alertness and performance at night, and provide a framework for eventual applications of circadian photobiological sciences in transportation lighting safety. More specifically, this literature review will investigate the effects of drowsiness on driver safety and how light can be used as a tool to reduce nighttime accidents by increasing driver’s alertness. Future research that is needed to elucidate the positive effects of light on driver safety will also be discussed. This novel and untapped approach could have significant, cost-effective implications for nighttime driving safety.