# Comparative Study of Energy Savings for Various Control Strategies in the Tunnel Lighting System
## 6 Conclusions  
It is essential that we decrease the electrical power consumed by the lighting installations in road tunnels, as well as the environmental and financial impact of these  
Figure 10: Choice of the control strategy for tunnels with different traffic volumes and lengths. installations. Despite those decreases, it is absolutely essential that these strategies do not impair traffic safety. Several groups around the world are currently working on this topic and some promising strategies are step-by-step being implemented. This study presents an evaluation and comparison of the initial installation costs and energy consumption of LED lighting systems using four tunnel lighting control strategies, a mix of traditional and intelligent. The assessment takes into account 100-day data collected in eleven tunnels in the Jilin Province, China with tunnel lengths between 650 m and 3200 m and traffic volumes between 750 and 2500. According to the results presented in this work, from a financial point of view, the tunnel length has a direct impact on the initial investment costs as well as the electrical costs; in return, the quantities of light sources, dimming controllers, optical transceivers, surveillance cameras, wiring, and auxiliary electrical devices (switches, transformers, etc.) increased with the increasing of tunnel length. For each control strategy, the energy consumption was estimated utilizing unit prices used by Chinese road agencies. The comparison between the initial installation costs demonstrated that the tunnel lighting system's cost for the ICS strategy is higher than those for the other three strategies. This is because of the increasing amount of equipment (e.g., LED luminaires, vehicle detectors, and surveillance cameras). Another important finding showed that the lighting consumption of the tunnel lighting system for the ICS strategy is lower than those for the other three strategies. This is because the operating time of the lamp is reduced as the luminance is controlled based on real-time environment luminance and vehicle presence. From the data presented in this study, in order to reduce the energy consumption and the environmental impact, it seems necessary to:  
* Replace the traditional lighting fixtures with high luminous-efficacy luminaires, in order to reduce energy consumption. * Adopt the LCL control strategy in the case of a lighting system service lifetime equal to or shorter than 218 days, in which the summary of initial investment cost and electrical costs is minimal, which is the most economical option. * Adopt the ICS control strategy in the case of a lighting system service lifetime equal to or longer than 955 days, in which the summary of initial investment cost and electrical costs is minimal, which is the most economical option. * Adopt an optimal control strategy between the DACS or ICS depending on tunnel length and traffic volume, in the case of a lighting system service lifetime between 218 and 955 days. * For newly-built tunnels that have relatively low levels of traffic, adopt the ICS pattern, which could minimize electric energy consumption, and in turn, contribute more to economic benefits. * For short tunnels, adopting the ICS pattern saves more energy than other control strategies. Thus, dividing newly-built long/extra-long tunnels into several short sections to adjust the luminance can achieve a more energy-saving effect. * In practice, several lighting control strategies could be combined to achieve the proposed energy saving according to the tunnel area segmentation/different time periods. In general, this study points out the optimum economical solutions for new tunnel constructions and retrofitting of existing tunnels. Conceptualization, L.Q. and J.-C.Y. ; methodology, L.Q. and A.P.-G.; software, L.Q. ; formal analysis, L.Q. and A.P.-G.; writing--original draft preparation, L.Q. ; writing--review and editing, A.S.L. ; funding acquisition, L.Q. and J.-C.Y. All authors have read and agreed to the published version of the manuscript.