In 1994, early drilling was conducted in the area. During 1999, full-scale construction work on the LBT commenced. It was largely excavated using a combination of traditional techniques, including drilling and blasting. Roughly 80% of the tunnel was built using these conventional practices. The remaining 20% was excavated using tunnel boring machines (TBMs). The excavation work was conducted from both the north and south portals. During April 2005, the construction process reached a milestone when breakthrough was achieved; the event was attended by 1,000 guests. The excavation process reportedly used 16 tons of explosives, while the material extracted would have filled a freight train that was 2,500 miles in length. Work over the following year centered on the fitting-out process, installing all of the operational systems, including the track itself.