Interesting! Found info to back this up. Would be good to have this note over the actual track ;-)

"The total length of the drill-and-blast tunnel is 13,295 metres, of which 5,864 metres is double track and 7,431 metres is single track.The double and single-track tunnels in the drill-and-blast section are horse shoe-shaped. The single-track tunnel is 6 m x 6 m wide with an average excavated section of 35 square metres. The tunnel holds one train track and a side walkway. The double-track tunnel is 10.8 m wide x 6.2 m high. It holds two train tracks and has a central partition wall with a walkway on either side.The tunnels are built from nine access points to achieve the tight programme so as to be ready between Sandton and the airport for the football World Cup in June 2010 and eight months later for the rest of the line. The underground section includes three deep stations (Park, Rosebank and Sandton), seven emergency access shafts (between 16 and 85 m deep) and one temporary main construction shaft (Mushroom Farm Park). The cover to the tunnel crown varies from approximately 15 m to 100 m.The 13,295 m drilled and blasted tunnel is excavated from 12 faces in total. Park station 1 face single track tunnel E2 shaft 2 faces single track tunnel Rosebank north 1 face single track tunnel E5 shaft 1 face single track tunnel Sandton south 2 faces single track tunnel double track tunnel Sandton station main cavern 1 face towards north Mushroom south 2 faces single track tunnel double track tunne Mushroom north 1 face double track tunne Marlboro 1 face double track tunne Each face is equipped with its own set of machinery comprising:Single-track tunnel one Robofore fully computerised jumbo (two booms and basket able to drill 4 m holes for face drilling and rock bolting). Robodrill supplied six similar computerised two-boom jumbos on a total of 17 for the project)."