Sichuan Baima Tunnel Lights Up

# Sichuan Baima Tunnel Lights Up

On September 29, 2025, with the official opening to traffic of the Jiawuhe–Wanglang section of the Jiuzhaigou–Mianyang Expressway, the Baima Tunnel—the longest and most critical control project along the entire route—was formally opened to the public. Buried deep within the Loess Ridge Mountains, this 13-kilometer-long super-long tunnel has not only earned a place in engineering history as “the most challenging construction project in China” but has also emerged as a shining gem on the northwestern Sichuan Plateau thanks to its intelligent lighting system. As night fell, thousands of LED lights inside the tunnel lit up like a galaxy, paving a safe passage for passing vehicles while illuminating the nine years of dedication and innovation by Sichuan’s transportation builders.

## Lighting Challenges in Passing Through “Tofu Rock Layers”

The construction of the Baima Tunnel has been nothing short of a protracted battle against geological hazards. The tunnel traverses seven fault-fracture zones, with Grade V surrounding rock accounting for as much as 97% of the total. The rock mass is predominantly carbonaceous slate and phyllite—soft, water-saturated, and easily crumbled at the slightest touch—earning it the engineers’ tongue-in-cheek nickname “tofu rock.” Under such geologic conditions, conventional blast-and-extraction methods are highly prone to triggering collapses, forcing the construction team to resort to non-blasting excavation techniques. Using tunnel-specific hydraulic breakers and excavators, they painstakingly chip away at the rock, achieving an average daily advance of less than 4 meters. To make matters even more challenging, the tunnel reaches a maximum burial depth of 1,092 meters, where high in-situ stresses cause continuous deformation of the rock mass; on one occasion, lateral displacement reached 1.5 meters in a single day, leading to repeated twisting and fracture of the installed support arches.

The design of the lighting system also faces significant challenges. In soft-rock environments characterized by substantial deformation, the mounting brackets for conventional luminaires are highly susceptible to loosening due to rock mass compression, which can result in luminaire detachment or angular misalignment. Furthermore, given that the tunnel section is entirely within a gas-rich zone, the lighting equipment must be explosion-proof and capable of effectively dissipating heat under the tunnel’s high-temperature and high-humidity conditions. To address these requirements, the construction team collaborated with a lighting manufacturer to develop a modular, explosion-proof LED luminaire. This luminaire features adjustable mounting brackets that accommodate rock mass deformation and is equipped with an intelligent temperature-control system, ensuring stable operation even at ambient temperatures as high as 38°C.

## Smart Lighting: From “Illumination” to “Protection”

The lighting system in the Baima Tunnel goes far beyond simply “turning on the lights.” More than 2,800 LED luminaires have been installed throughout the tunnel, featuring a “chevron” longitudinal profile that automatically adjusts brightness based on external light levels. The entrance section boasts the highest light density—one luminaire every 10 meters—to help drivers’ eyes quickly adapt to changes in lighting conditions; in the middle section, the spacing between luminaires gradually increases to 20 meters, balancing illumination needs with energy savings; and at the exit, the lighting mimics a gradual transition to natural daylight, thereby reducing the risk of glare caused by the “white-hole effect.”

Even more striking are the anti-fatigue lighting fixtures installed inside the tunnel. Mounted on the sidewalls on both sides at 3-meter intervals, each set projects local cultural IP content and is controlled remotely via the international DMX512 protocol, creating a visual feast for drivers as they pass through the tunnel and helping to prevent fatigue caused by prolonged driving.

In addition, an intelligent lighting control platform has been deployed within the tunnel. Leveraging the “Sichuan Tunnel Large Model,” the system performs real-time analysis of traffic volume, vehicle speed, and weather data to dynamically adjust lighting strategies. For instance, during rainy or snowy conditions, or when visibility drops below 500 meters, the system automatically increases illumination intensity at the tunnel entrance; at night, when traffic volume is low, it reduces brightness in the mid-section to conserve energy. According to estimates, this system can cut annual electricity costs by approximately RMB 1.2 million, equivalent to a reduction of 800 metric tons of carbon emissions.

## Harmonious Coexistence of Ecology and Technology

The lighting design for the Baima Tunnel has consistently integrated the principle of ecological conservation. The tunnel is strategically located deep beneath the loess-ridge ecological corridor, thereby minimizing disturbance to surface vegetation and wildlife habitats. To mitigate light pollution, the tunnel portals feature a “bamboo-slit” design that directs light inward, preventing it from spilling outward and thus avoiding interference with the nocturnal activities of rare species such as giant pandas and golden snub-nosed monkeys. In addition, all interior lighting in the tunnel employs cold-light sources that emit no ultraviolet radiation, thereby reducing insect attraction and preserving the ecological balance.

During the construction phase, the lighting team also pioneered the innovative application of “light-guide illumination” technology. A set of daylighting domes is installed every 200 meters along the tunnel roof, using optical fibers to channel natural light into the tunnel maintenance accessways. During the day, this system can fully replace artificial lighting, delivering significant energy savings while creating a more comfortable working environment. This technology represents the first such application in highway tunnels nationwide, setting a green construction benchmark for similar projects.

## The Beacon of Future Transportation

Today, as vehicles enter the Baima Tunnel, soft, flowing light bathes the interior, creating a striking contrast with the snow-capped Min Mountains beyond. Once deemed “impossible to build” by geological experts, this tunnel has not only overcome a world-class challenge through technological innovation but has also redefined safety standards in tunnel engineering with its human-centered lighting design.

For truck driver Master Zhang, who commutes daily between Jiuzhaigou and Mianyang, the lighting system in the Baima Tunnel provides him with great peace of mind: “In the past, taking the old national highway and crossing Huangtuliang used to take more than three hours, and the icy road surface in winter was especially dangerous. Now the tunnel is bright and warm, and it only takes 20 minutes to drive through—no longer do I have to worry about driving at night.” Data show that, since the tunnel opened to traffic, the accident rate on this section of road has dropped by 76%, while traffic efficiency has tripled.

From its groundbreaking on April 29, 2016, to the completion of twin-tube breakthrough on December 12, 2024, and finally to its official opening to traffic on September 29, 2025, the Baima Tunnel has borne witness to the Sichuan transportation builders’ spirit of “blazing trails through mountains and overcoming all obstacles.”

The successful completion of the Baima Tunnel has not only set a new benchmark for transportation infrastructure development in Sichuan Province but has also become a shining emblem of tunnel engineering on a national and even global scale. Its innovative application of an intelligent lighting system has significantly enhanced driving safety and comfort while delivering outstanding results in energy conservation, emission reduction, and ecological protection, thereby providing invaluable experience for sustainable development. As the “Building a Transportation Powerhouse” strategy continues to advance, the pioneering spirit embodied by the Baima Tunnel—“blazing trails through mountains and building bridges over rivers”—is inspiring more engineers and constructors to scale new technological heights and tackle increasingly complex, world-class engineering challenges. Looking ahead, with the implementation of more similar projects, we can confidently expect that the level of intelligence and greenness in China’s transportation infrastructure will continue to rise, delivering safer, more convenient, and more efficient travel services to the public. At the same time, the Baima Tunnel will serve as a vital bridge connecting nature and culture, technology and ecology, continuing to shine across the northwestern Sichuan Plateau and illuminating the path toward a brighter future for transportation.