Within the scope of Project, Doğuş completed the construction of the tunnel with a total length of 5.97 km long between 8 km and 8 stations of Krasno Selo and Hadji Dimitar districts. A giant Tunnel Boring Machine (TBM) with an excavation diameter of 9,39 meters, uniquely manufactured by Doğuş Construction, was used for the construction of the tunnel.

Doğuş Construction, which has been operating in Bulgaria since 2003, has successfully completed its third-largest project in Bulgaria, one of the highway and two of the metro lines. On the other hand, Doğuş Construction completed the 45-kilometer part of the international Thrace Highway, located in the east of the country, between the cities of Burgaz and Karnobat, in 2008. Doğuş Construction, which completed the construction of 4 most prestigious metro stations of Sofia with a length of 3.8 km in 2012, was awarded the "Building of the Year" Award with the "Lion Bridge" and "Serdika II" stations