China opens first urban cross-sea bridge rail line

In line with the national deployment in building new infrastructure, Ningbo — a semi-provincial-level coastal city in Zhejiang province — opened a new urban rail transit line on Tuesday to promote its intracity integrated development.

The Ningbo-Xiangshan intracity line, a 61.45-kilometer subway with 10 stations — two underground and eight above ground — links the city proper with Xiangshan county, with trains running at a maximum speed of 160 kilometers per hour.

Ningbo Rail Transit Group Co Ltd, owner of the line, said that by traversing the East China Sea and Xiangshan Port, the rail can quickly link the towns, industries and cultural tourism resources along the route into the Ningbo metropolitan area.

It said the line's most eye-catching project is the Xiangshan Port cross-sea bridge traversing the East China Sea, which extends for 8.276 km, including a main bridge length of 1,376 meters and a main span of 688 meters.

"It is the first cross-sea bridge on an urban railway in China and currently the world's largest ballastless-track cable-stayed railway bridge," said Zhang Chuanbo, manager of the construction project from the China Railway No 4 Engineering Group (CREC4), which helped lay the rail tracks on the entire bridge.

"The railway bridge and the existing cross-sea highway bridge traverse Xiangshan Port in parallel, forming a unique landscape," Zhang said.

The whole line, starting from Xiaoyangjiang Station in Yinzhou district in the north and crossing the Xiangshan Port, enters Xiangshan county before finally reaching Damuwan Station.

Ningbo Rail Transit stressed that the fastest travel time from Ningbo's urban area to Xiangshan county is approximately half an hour, greatly bolstering the convenience of travel.

CREC4 undertook the construction tasks of the main line and wiring between Xiaoyangjiang Station and the starting point of Zhuangxi Dashan Tunnel, Yunlong rolling stock depot entrance and exit lines, as well as related elevated bridge deck waterproofing.

Bai Lin, chief engineer of the CREC4 project in laying rail tracks on the bridge and a staffer of CREC4 Eighth Engineering, said they began to lay tracks on the bridge on Oct 6,2025.

"The most difficult and dangerous task along the whole line was laying tracks on the Xiangshan Port cross-sea bridge, as it is only 50 meters away from the existing cross-sea highway bridge as well as a semi-floating system," said Hu Jiaman, director of the engineering division of the CREC4 project department.

"Under temperature and wind loads, the deformation is complex, and strict millimeter-level requirements are needed for the smoothness of the ballastless tracks," Hu said, adding that laying ballastless tracks on such a bridge is like drawing a straight line on shaking paper.

He said their project department developed a high-precision vertical deformation monitoring model by partnering with researchers from Southwest Jiaotong University, helping dynamically calculate the optimal construction alignment in real-time by integrating temperature, wind speed, load and related data.

Dang Ben, head of the 4th engineering team of the CREC4 project department, led his team members to squat on the bridge deck, staring at the jumping numbers of the instruments and gradually grasping the "temperament" of the bridge.

After the official handover of the main bridge of the cross-sea bridge, the job of laying ballastless tracks began instantly, Dang said, adding that as 538 prefabricated track slabs were successively hoisted onto the bridge, he and his colleague Yang Xiao led two teams working around the clock to finish the job.

Bai stressed that the secret to the smooth and high-speed passage of trains with a maximum speed of 160 km/h on the cross-sea rail bridge mainly relied on three elements.

Firstly, the bridge foundation is deep, as the main bridge used 108 ultra-large diameter bored piles, with a maximum pile diameter of 3.5 meters and a maximum depth of 122 meters, he said, explaining that this is equivalent to driving a 40-story-high "giant nail" into the seabed to stabilize and support the bridge piers.

Secondly, as the new bridge and the old bridge run parallel, with a distance of only 50 meters apart, the builders had to ensure the structures will not interfere with each other, so they skillfully managed wind resistance.

"The builders have conducted more than 20 wind-tunnel tests, undergone hundreds of tests, and ultimately optimized the shape of the new bridge by setting up a three-meter-high diversion wind barrier to effectively suppress vortex vibration on both bridges," Bai said.

Thirdly, accurate vibration reduction can be controlled, he said, noting that they innovatively used 78 dampers to largely improve bridge damping and ensure the smooth and safe passage of high-speed trains.