SHANGHAI is considering building a network of additional subway to form a "virtual ring" to ease the pressure on Metro Line 4, the city's only ring-shaped Metro line, a senior planning official said yesterday.

The planned underground network will essentially connect new townships in the suburbs to existing ones to make it easier for commuters to change lines, Shi Jiaming, deputy director of the Shanghai Planning, Land and Resources Administration told lawmakers yesterday.

"To save costs, the new 'line' will share stations with other lines to create a new ring route," Shi said. "It will be a 'virtual ring' rather than like the actual ring-like Line 4."