the escalator shafts. Thiess and Hochtief delivered the project as a joint venture which included the design and construction of a driven railway and four fully mined stations. The line consists of two tunnels – one for each track. The tunnels were constructed using two tunnel boring machines, with a section underneath the Lane Cove River being constructed by the cut and cover method (next to where Delhi Road crosses the River). The line is fully bi-directional, with three crossovers to allow trains to switch tracks in the event of a disruption. The tunnels include a walkway on one side, at platform height. Several associated works were also completed to coincide with the opening of the new line. These include the rebuilt Chatswood interchange, a major upgrade at Epping, an upgrade of North Sydney station, the Hornsby turnback Rail Clearways project and new substations at Waverton and Beecroft. Issues In December 2007, it was announced that Tangara trains would not be running on the line due to steepness of the tunnel. The line owner, RailCorp, has denied that this is an engineering bungle, saying "The Tangara trains, because they are not ideally suited to that steep gradient, will not be allocated to that line even though they can operate." S set trains were also excluded, due to concerns over possible problems performing "push-out" duty (a loaded train pushing out another loaded train) on the gradients. In February 2008 it was revealed that mats, connected to the rail tracks and concrete slabs to reduce noise, had separated and needed to be replaced, with at least half of the of track to be re-laid. On 23 October 2008 it was also confirmed during testing that sound levels on the train were 90 decibels, as loud as a 737 plane coming into land. Plans to rectify this would come at a cost that has already blown out from $1.4 billion to $2.3 billion. In July 2009 it was reported that drivers were being restricted to two return shuttle runs through the tunnel before taking a break as well being instructed to keep the lights on in the driver's cabin and lower the side window blinds in order to avoid a possible stroboscopic effect caused by the tunnel lighting, with claims it may have caused headaches, dizziness, fatigue and nausea. Initial service The line opened on 23 February 2009 as a shuttle service between