# Comparative Study of Energy Savings for Various Control Strategies in the Tunnel Lighting System
###### Abstract
[16] used solar optical fiber lighting to enhance tunnel lighting, reduce energy consumption, and improve lighting quality and environmental protection, whereas [PERSON] et al. [17] and [PERSON] et al. [18] used light pipes for this same purpose. [PERSON] and [PERSON] [19] developed a new system for improved illumination by using enhanced parallel sunlight on the tunnel entrance. This system achieved highly efficient and long-distance sunlight transportation through optical path transformation and reflection. [PERSON] et al. [20] proposed a solar power supply system that used solar photovoltaic power generation based on hybrid wind-solar power generation. [PERSON] [21] proposed an energy-saving power supply system based on wind-light complementary and hybrid energy storage. These authors used solar energy to provide lighting at the tunnel entrance and wind turbines at the top of the tunnel to complement the tunnel's power supply system. [PERSON] [22] proposed the SLT equation, which established the theoretical basis to foresee energy savings and calculate the necessary parameters with any strategy using sunlight in road tunnels from either perspective, i.e., shifting of the threshold zone and/or direct injection of light inside the tunnel. 3. Then, there is the option to install or retrofit the lighting system with cost-effective luminaires to balance the energy consumption and provide adequate luminance. LED luminaires provide notable benefits of long life, high luminous efficiency, short start-up time, low power consumption, and high color temperature. These luminaires are already being applied to replace conventional light sources for tunnel lighting [23; 24; 25]. [PERSON] et al. [26] used a mixture of high-pressure sodium (HPS) lamps and LEDs in the tunnel threshold zone to reduce the high costs. [PERSON] et al. [27] compared the economic performance of LED and HPS lamps for road lighting. The results showed that LED lighting has a better performance than HPS luminaires due to decreased operating costs and increased savings; thus, there is a larger potential for improving road safety using cost-effective LED lighting. [PERSON] et al. [28] presented findings that better visibility in the tunnel can be achieved by increasing the luminance uniformity of LED under the equivalent luminance, saving up to 20% electric energy. [PERSON] [29] studied the differences in luminance and energy costs of the Huayingshan tunnel when replacing HPS with LED luminaires. The results showed that the LED lighting system could save as much as 63.6% in energy costs. In parallel with the abovementioned three main strategies, which are compatible among themselves, it is also effective to provide devices to guide drivers' sight in tunnels and improve drivers' visual adaptability. [PERSON] et al. [30; 31] proposed that setting delineators in tunnels could change the monotonous environment and increase drivers' attention, decreasing drivers' anxiety and mental workload and ensuring their driving safety. [PERSON] et al. [32] investigated the effect of reflective ring numbers on drivers' curvature perception at different radii tunnels using a driving simulator. The experimental results showed that drivers' reaction times slightly decrease when using reflective rings. In particular, three reflective rings are recommended because they can effectively improve drivers' curvature perception and control the reaction time within a reasonable range. [PERSON] et al. [33] designed three groups of comparative experiments using a driving simulator to investigate the influence of signs and markings on drivers' movement. The experimental results showed that a thin red pavement and speed limit sign before the tunnel entrance significantly affected the speed standard deviation's control. However, the sightline guidance system's setting lacks a basis; it is difficult to unify the size, installation distance, and sightline guidance facilities' combination due to a lack of reference standards [34].