Physiological reactions during the tunnel driving under various illumination conditions were studied to assure the safe driving. Heart rate of the driver increased by 60-80% of the resting level while driving through the tunnel.
If the tunnel lights were experimentally turned off but immediately put on again, no significant increase of heart rate was observed. Heart rate increase was as low as 10-20% if the switching-off of the lights was short and had been expected.
Unexpected turning off of the illuminaton some-times caused abnormal rise of heart rate, accompanying inadequate driving performances. It was concluded that the poor illumination, abrupt change of the brightness or lack of emergency power supply are relevant to higher accident rate and should be avoided.