It is situated between Vezirhan and Bilecik bypassing the Gülümbe Pass with hairpin turns. The 745 and 840 m (2,444 and 2,756 ft)-long twin-tube tunnel carries two lanes of traffic in each direction. The 2,465 and 2,474 m (8,087 and 8,117 ft)-long Osmangazi Tunnel is located south of it. The highway Mekece-Bilecik-Bozüyük on the north-south directed D.650 at a distance of 86 km (53 mi) is a heavy traffic route for transport of industrial and agricultural products connecting the regions Marmara, Aegiean, Central Anatoli and Mediterranean.[1]
In 2000, a financial agreement was signed between the Turkish and Japanese governments to build a divided highway with two tunnels at the steep pass. Construction works on the highway began in 2003, and in 2010 the route was put into service.[1] The tunnel was initially named Kaletepe Tunnel, but was renamed in 2009 in honor of Ertuğrul Gazi (1191–1281) the father of Osman I, the founder of the Ottoman Empire.[2]
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