The extension of the airport runway across the state border to Schleswig-Holstein in the 1960s cut through the Garstedter Weg, the connection from Niendorf to Garstedt. The Krohnstieg Tunnel was built as a replacement. This also improved road connections in the north of Hamburg. A new road, part of Ring 3, from the "Schnelsen-Nord" junction on the A 7, was built to the tunnel, which was extended on the eastern side to Langenhorn. With the expansion of the airport from the 1990s and the construction of the Fuhlsbüttel bypass, the Krohnstieg Tunnel was also extended. To the north of the old road tunnel, a second tube was built using open construction between 1995 and 1998, so that two lanes are now available in each direction. The necessary demolition and reconstruction of the runway took place in just five months in order to have as little impact on flight operations as possible. The original Krohnstieg tunnel consists of a two-lane tube for road traffic, around 419 meters long and ten meters wide, and a six-meter-wide tube to the south for pedestrians and cyclists only, with a slightly higher floor. The ramps on the sides are 415 meters long. With the completion of the second tube for road traffic in 1998, the tunnel took on its current appearance.
The tunnel is a closed reinforced concrete frame. Like the entire airport area, which belongs to Hamburg, it is located in the Fuhlsbüttel district. The western portal is in Niendorf, the eastern one in the area of the city of Norderstedt.