The Turkish bid was the cheapest of the nine submitted, at EUR 89.3m, excluding VAT, according to information posted on the public contracting portal on Friday.
The deadline for potential complaints against the pick, made by DARS, the state-run motorway company, on 30 July, expires on 16 August.
The notice says that an examination of the most economical bid and amendments and explanations by the Turkish bidder showed that Cengiz Insaat Sanayi Ve Ticaret met all the terms and conditions.
The bid was established to have been submitted on time, met the investor's needs and requirements, and was not estimated as unusually low.
The highest bid, at EUR 140.3m, was submitted by Slovenian builder Pomgrad in conjunction with Swiss group Marti. The bid was eliminated because it exceeded the project's estimated value of EUR 121.5m.
The second lowest bid was submitted by Slovenian builder Gorenjska Gradbena Družba, in cooperation with its Czech counterpart Metrostav. They offered to build the Slovenian part of the tube for EUR 104.4m.
A contract with the selected bidder cannot be signed until after the procurement decision becomes final.
The entire project involves the construction of a new, 3,546-metre motorway tube and a 620-metre motorway section connecting the tube to the existing motorway.
The investment is estimated at EUR 151.6m, VAT excluded, of which construction is budgeted at EUR 121.5m. The construction is estimated to take five years.