A constructor works at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Constructors work at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Aerial photo taken on July 29, 2020 shows the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Constructors work at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Constructors work at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Aerial photo taken on July 29, 2020 shows the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

A constructor works at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Constructors work at the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province, July 29, 2020. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)

Aerial photo taken on July 29, 2020 shows the construction site of China's first tunnel across the Yellow River in Jinan, east China's Shandong Province. Located in Jinan, the 15.76-meter-diameter tunnel is the country's widest shield tunnel for both rail and road transport. With a total length of 4.76 km, the tunnel contains two levels. A two-way six-lane highway is on the upper level and the lower level is reserved for rail transit, flues and escape channels. (Xinhua/Wang Kai)