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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 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, highwaytunnel safety, Markov chain

As a component of the traffic control plan, traffic signs on highways offer drivers necessary information. Unfortunately, many signs are unfamiliar to or misunderstood by drivers, especially when lacking a setting method; this includes exit advance guide signs in tunnels. These are generally set in roadbed sections, but space limitations in tunnels dictate that they must be set differently. To evaluate the effect of the setting method, an experiment was designed and conducted, during which the eye movements of 44 drivers with different familiarity levels were tracked. Twenty-two of the drivers had not previously participated in any experiment involving exit advance guide signs in highway tunnels, while 22 of them had. Time period data were analyzed, including data from before the sign appeared, when it appeared, and when it disappeared. Based on area division and Markov theory, attributes related to gaze transition were obtained, including one- and two-step gaze transition probabilities and area gaze probabilities. The results showed that gaze transition was confirmed to be significantly different between the three periods and between the drivers. Features extracted from eye movement characteristics, gaze transition paths, and gaze areas demonstrated that visual attention is more dispersed in familiar drivers during the lane-change intention period. Therefore, signs should be placed on the left wall of the highway tunnel.

Exit Advance Guide Signs play an important role in driving safety on highway tunnels. With the increase of mountain highway in recent 10 years, how to set exit advance guide signs inside the mountain highway tunnels become a new problem in China. The paper highlighted the influence of exit advance guide signs on the driver's eye movement in the mountainous highway tunnel. Specially, exit advance guide signs in the mountainous highway tunnel were divided into two separate signs: one was location sign, which set on the top of tunnels by Chinese characters with height of 40 cm and width of 20 cm; the other was distance sign, which set 62.6 m away the location sign, with a character height and width of 1.5 m, and a total sign length of 22.5 m. Six schemes of different height, width and spacing were tested, in which the distance sign was on the left or right wall of the tunnel, and the vehicle was on the left lane. A Markov chain was used to analyze the driver's eye movement characteristics to evaluate the effect of separate guide signs. The results were as follows: when the distance sign was set on the left wall, the scheme with height, width and spacing of 1.5m was the best choice. When the distance sign was set on the right wall, the scheme with height, width and spacing of 2m was the best choice. This study can optimize exit advance guide signs setting in the mountainous highway tunnel, then contributing to reduced traffic accidents and making mountain highway transport more sustainable.