Drivers' Saccade Characteristics in Curves of Extra-Long Urban Underwater Tunnels

Traffic accidents in extra-long urban underwater tunnels are characterized by high numbers of causalities and severe traffic congestion. Analyzing drivers' saccade characteristics under different curvature conditions in urban underwater tunnels can provide solutions to reduce the rates of such accidents and increase traffic safety. This paper reports real vehicle tests conducted in extra-long urban underwater tunnels, on curved sections of radii of 400, 680, 1,000, 1,500, and 3,000 m, and also on straight sections. Indicators of drivers' saccade behavior, such as saccade angle, time, and frequency, and the saccade time ratio were evaluated. The coefficient of variation was used to analyze the discreteness of the saccade angle. The driver's saccade characteristics, such as saccade time and frequency, were explored by combining the visual distances for different curved sections. The results demonstrated that (a) small angles in the range of [0, 10 degrees] constituted the main distribution section of the driver's saccade angle in extra-long urban underwater tunnels, and the saccade angle discreteness increased with increase in the radius, (b) the driver's average saccade time increased while the average saccade frequency decreased with the increase of the radius, (c) the driver's visual load was higher for long straight sections and small-radius curves, (d) the driver's safety was generally higher on right-curving sections than on left-curving sections.