Review on evaluation and optimization of light environment of extra-long urban underwater tunnel based on visual demands

To improve the traffic safety and transportation efficiency of extra-long urban underwater tunnels, the typical problems and improvement measures of light environment in extra-long urban underwater tunnels were summarized. From the aspects of comfort, economy, setting basis, and installation form, four kinds of improvement measures of light environment of tunnels were compared and analyzed, including shading facilities at the entrance, enhanced lighting at the entrance and exit, landscape decoration, and visual induction system. Drivers' visual demands were stratified according to the theory of Maslow's hierarchy of needs. The research framework of the light environment evaluation system and optimization of extra-long urban underwater tunnels was proposed, including the accident analysis, evaluation system, optimization idea, and optimization method. Analysis result shows that the light environment of extra-long urban underwater tunnels mainly has the issues of light and dark adaptation at the entrance and exit, insufficient sight distance caused by changes in the road alignment, the lack of visual reference information in the middle, and the unclear right of way in the overall space of the tunnel. The setting of a visual induction system is a low-cost and effective method to optimize the light environment, which can meet the drivers' visual differentiation needs in different tunnel sections. Drivers' visual demands can be divided into function, safety, comfort, and esthetics from low to high corresponding to the fundamental, safe, comfortable, and rhythmic visual reference systems. The evaluation system can be constructed to evaluate the light environment of extra-long urban underwater tunnels with the indexes of space right of way, human factors, driving tasks, differentiation, and rhythmicity. The light environment optimization of extra-long urban underwater tunnels should combine visual induction with enhanced lighting, while the visual induction system is mainly used to reconstruct the visual reference system. A comfortable visual reference system should be considered as the optimization target in the access zone, threshold zone, interior zone (general area), and exit zone of the tunnel, while the rhythmic visual reference system should be built in the interior reminding and awakening areas. 10 tabs, 8 figs, 43 refs. © 2020, Editorial Department of Journal of Traffic and Transportation Engineering. All right reserved.