While the number of highway tunnels is increasing, the current Chinese criteria and Uniform Traffic Control Equipment Manual (MUTCD) 2009 guidelines provide no clear method for setting exit advance guide signs in highway tunnels. To solve this problem, this paper proposes separate guide signs, consisting of location and distance signs. Location signs on the tops of tunnels use Chinese characters with a height of 40 cm and a width 20 cm. The distance signs are 62.6 m from the location signs with

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... a character height and width of 1.5 m and a total sign length of 22.5 m. Four schemes were tested, in which the distance sign was on the left or right wall of the tunnel and the vehicle was in the left or right lane. At the "Perception" and "Recognition" stages, the pupil area change rate of the four schemes had a slight difference to no sign but were always less than the 20% threshold line. A Markov chain was employed to analyze the driver's eye movement characteristics to evaluate the effect of separate guide signs. The results are the following. In the left lane, when a distance sign on the left wall of the tunnel appeared, the driver's fixation points were relatively balanced, except in the left area. After the sign disappeared, the driver's fixation points were no different than before, except in the front area. However, when a distance sign appeared on the right wall, 77.84% of the driver's fixation points were concentrated in the front and right areas, which decreased the driving safety. Similar results were obtained in the right lane. Therefore, distance signs should be placed on the left wall of the highway tunnel. This study can forewarn a driver in a tunnel of the exit location and distance and help the driver to exit the highway safely. INDEX TERMS Exit advance guide sign, highway sign recommendations, driver's eye movement, highway tunnel safety, Markov chain. B. RELATIONSHIPS BETWEEN EYE MOVEMENT, TRAFFIC SIGNS, AND TUNNELS More than 80% of the information obtained by a driver is derived from vision [15] . Visual behavior consists 24080 VOLUME 9, 2021