As a part of the Bundesautobahn 7 in Hamburg, the tunnel forms a connection between Schleswig-Holstein (and on towards Denmark) to the north and Lower Saxony to the south.

The newest, fourth bore is the only one to feature a hard shoulder, minimizing congestion due to broken down vehicles.

To meet the demands of increasing traffic, on 27 October 2002 a fourth bore was opened with two more lanes.The total cost for this expansion amounted 550 million euros.

[1] It had been drilled through the ground by the then world's largest tunnel boring machine (TBM), which had a front plate 14.65 m (48 ft 1 in) in diameter.

The centre bores carry reversible lanes which switch direction in anticipation of commuter flows, similar to those of Caldecott Tunnel in Oakland, California.