A new tunnel section was built to avoid dangerous cliffs in Japan's Kariba Tunnel, while keeping traffic flowing. The construction methods used included movable protectors and high-strength concrete lining. These methods were developed to widen tunnels with small cross-sections and shorten construction times. Improvements are proposed to make the process faster and more efficient, including developing lighter protectors and different-shaped precast lining plates. These advancements aim to make tunnel excavation and operation faster and safer, ultimately improving the working environment for construction workers.