The two parallel pipes from Pudong to Puxi yesterday signal all systems go. The Xizang Road S. Tunnel is the city's steepest and specially designed for the Shanghai World Expo 2010.

Shanghai's new World Expo 2010 tunnel will be the city's steepest as it has to run beneath a subway tunnel across the Huangpu River, project engineers said yesterday as drilling started on one of the tunnel's two parallel shafts from Pudong to Puxi.

"Drivers will find it will be like driving down into and then out of a valley," said Pan Guoqing, the senior engineer of Shanghai No. 2 Municipal Engineering Company is in charge of the project.

He said the gradient of the new tunnel, called Xizang Road S. Tunnel, will reach five degrees while most of the city's present tunnels' have gradients of about three to four degrees.

Pan said right above the the tunnel is another tunnel, a section of the Metro Line 8, which links Yangpu District with downtown stations.

"Our tunnel is only 2.8 meters lower than the subway tunnel," Pan said. However he said there should be no technical problems that will prevent the builders finishing the tunnel in time to streamline traffic flow for the World Expo.

Located in the center of the 5.28-square-kilometer Expo site between the Nanpu and Lupu bridges, the tunnel will span 2.67km and link Xizang Road S. in Puxi with Pudong Road S. on the river's eastern bank.

When it opens the tunnel will carry only Expo traffic but after Expo the tunnel will be open to the public.

The tunnel will incorporate two shafts, each of which includes two traffic lanes. The two lanes in one shaft go south to north and the other two in the other shaft vice versa.

City officials expect 70,000 people to cross the Huangpu River every hour during the six months of World Expo.