title: Metro Tunnel
context: The Metro Tunnel (sometimes also known as the Melbourne Metro Rail Project or the Metro Rail Capacity Project) is a metropolitan rail infrastructure project currently under construction[1] in Melbourne, Australia. It includes the construction of twin 9-kilometre rail tunnels between South Kensington station (north west of the Melbourne City Centre) and South Yarra (in the south east) with five new underground stations. The southern portal for the tunnel is to be located to the south of South Yarra station. As a result, the tunnel will connect the Pakenham and Cranbourne lines with the Sunbury line, and allow these lines to bypass Flinders Street station and the City Loop while still stopping in the Melbourne central business district.
question: How long is the Melbourne Metro Tunnel going to be?
answers: 9-kilometre