It was learned on May 12 that the Qinling Tiantai Mountain extra-long tunnel, the world's largest in construction scale, has entered the asphalt paving stage. Once asphalt paving is completed and signage, markings, and electromechanical facilities are installed, the Baoping Expressway will enter the acceptance stage for opening to traffic.

The main line of the Baoping Expressway is 73.238 kilometers long and is built to a two-way, six-lane expressway standard. The Qinling Tiantai Mountain ultra-long tunnel group, the controlling project of the entire line, has a total length of 32 kilometers, with bridges and tunnels accounting for 98.1 percent. It is an ultra-long continuous longitudinal-slope tunnel group featuring notable engineering characteristics such as "multiple lanes, great burial depth, connected bridges and tunnels, and extra-long tunnels." Among them, the Qinling Tiantai Mountain extra-long tunnel is 15.56 kilometers long with a maximum burial depth of 973 meters and is a two-way, six-lane separated tunnel.

The pavement of the Qinling Tiantai Mountain extra-long tunnel is designed as an asphalt concrete composite pavement. Paving adopts a single-machine full-width one-pass molding construction technique. The middle and upper surface layers use warm-mix asphalt technology, and the upper surface layer uses SMA asphalt mixture with flame retardants added, making it currently the largest tunnel asphalt composite pavement project under construction in China. The promotion of the application technology of the safe flame-retardant asphalt pavement in the Qinling Tiantai Mountain extra-long tunnel has effectively improved the smoothness, construction efficiency, and skid resistance of the ultra-long tunnel pavement, and has important guiding significance for improving tunnel pavement construction techniques in China's long and extra-long tunnels and areas with harsh climates. Its energy-saving and environmental protection effects are remarkable, greatly enhancing later operational safety and driving comfort for drivers and passengers.

Since construction began in October 2016, the Baoping Expressway construction project achieved high-precision breakthrough of the Qinling Tiantai Mountain extra-long tunnel on December 28, 2020, setting a new historical record for the construction of multi-lane tunnels on Chinese expressways and creating another super project in the world's highway tunnels. As of now, the entire line has completed a cumulative investment of 12.06 billion yuan, accounting for 93.5 percent of the estimated investment. The subgrade, bridge, and tunnel works and the building construction and landscaping works have all been completed. The pavement, electromechanical, and traffic safety projects are under construction. Once asphalt paving is completed and signage, markings, and electromechanical facilities are installed, the Baoping Expressway will enter the acceptance stage for opening to traffic, ensuring the entire line is completed and opened to traffic in October and connecting the Shaanxi section of the Yinchuan-Kunming Expressway.