The tunnel was constructed in the 1980s . During the 1999 İzmit earthquake , the tunnel was light damaged . In 2012 , the tunnel 's both tubes were reinforced . In the time period of 2013 – 2014 , the tunnel was modernized for traffic safety . Around 55,000 vehicles pass through the tunnel in both directions daily
1999 İzmit earthquake
1999 İzmit earthquake
Gültepe Tunnel