The Rennsteig Tunnel crosses under the ridge of the Thuringian Forest with the Rennsteig ridge trail. It is the longest road tunnel in Germany and one of the longest in Europe. It was opened in 2003 and is part of the A 71 highway, which connects Erfurt with Schweinfurt. The tunnel has two tubes, each with two lanes and emergency lanes. It has a modern ventilation and safety system that ensures air quality and traffic flow.