Review and Thinking on Landscape Design of Highway Tunnel

Because of the unique structure of highway tunnels, traffic accident and mortality rates of highway tunnels are higher than those of ordinary sections. An appropriate tunnel landscape can alleviate drivers' discomfort, and a reasonable tunnel entrance landscape can effectively ease drastic changes in the driving environment, improving driving safety. Tunnel landscapes are arbitrary during the design process, and the effect is difficult to control, owing to the lack of an established design system and detailed specifications. Some landscape designs do not fully consider driving characteristics; therefore, the role of the tunnel landscape in driving safety is unclear. Based on the design and research state of tunnel landscapes, driving safety and comfort, the tunnel entrance landscape (portal appearance, entrance greening, and entrance signs), and the tunnel hole landscape (vault and sidewall landscape, tunnel pavement, and tunnel landscape zone) were analyzed and summarized. Corresponding design recommendations were proposed, and urgent problems encountered in tunnel landscape design were analyzed. The results show that the appearance design of a highway tunnel portal should reflect not only a single element but also the superposition effect of different elements. However, research on the appearance of highway tunnel portals has not been conducted extensively, and effective evaluation indices are required for all types of unique portal appearances to achieve quantitative analysis. Greening at the tunnel entrance can effectively enhance driving comfort and alleviate the brightness difference inside and outside the tunnel. Rich greening should be implemented as much as possible to beautify the tunnel entrance. However, the selection of plant species, collocation of plants, and quantification of plant spacing need to be systematically investigated. The tunnel nameplate design is random, which may have a negative effect if the nameplate is poorly designed. Billboards and slogans should not be placed at tunnel entrances. In tunnels, the landscape design of the vault and side wall should break through inertia thinking and actively apply light colors and suitable pattern decoration. It is necessary to quantitatively analyze the location, color, length, and form of the pavement to clarify the role of colored pavements in tunnels. The landscape zone in the extra-long tunnel can effectively relieve driving fatigue; however, parameters such as location, spacing, and length need to be further investigated. Because of problems in the research methods of highway tunnel landscapes, some suggestions in terms of research approach, tester selection, and research indicator selection are proposed. © 2022, Editorial Department of China Journal of Highway and Transport. All right reserved.