DALIAN, May 1 -- An undersea road tunnel opened to traffic on Monday in Dalian, a coastal city in northeast China's Liaoning Province.

The tunnel, accommodating a two-way six-lane urban expressway beneath Dalian Bay, is the first immersed tube undersea tunnel in north China, said Sun Zhu, deputy chief engineer of Dalian Bay Undersea Tunnel Co., Ltd., which is in charge of building and operating the tunnel.

The designed traffic speed in the 5.1-km tunnel is 60 km per hour, said Sun. Construction of the tunnel took some four years.

The road connecting the tunnel went operational on Monday, linking the northern and southern coasts of Dalian Bay, helping to alleviate traffic congestion and expand the space for urban development in Dalian.