Sinking
The most common method of tunnelling if a river needs to be crossed is sinking (of sinking down). On the HSL, this is the case at the Oude Maas and the Dordtsche Kil. The prefabricated tunnel components are sunk down into a dredged ditch in the riverbed. This method is used for most tunnels in the Netherlands: the Maas Tunnel, the (first) Heinenoord Tunnel, the Drecht Tunnel, the Willem Rail Tunnel and the second Benelux Tunnel. If these tunnels had to bored through the riverbed, the tunnel would be situated considerably lower, making it longer as well.

In order to spare the Green Heart Area and its valuable scenic landscape, it was decided to make a deep, bored tunnel here. The result is a unique construction: its diameter of almost 15 metres makes it the largest bored tunnel in the world in terms of diametre.

Bored tunnels are popular, because they cause less damage and inconvenience than cut & cover tunnels. The Second Heinenoord Tunnel, the Botlek Tunnel under the Oude Maas river, the Westerschelde Tunnel, the Tram Tunnel in the Hague, and the 50-kilometres long Channel Tunnel, are examples of bored tunnels. 

The surroundings of the Rotterdam North Fringe Tunnel is best suited for digging, using the cut & cover method. The tunnel roof is only 2.5 metres deep and in such a situation, digging is much more cost-efficient than boring. Another advantage is the tunnel diameter, which is not restricted by the diameter of a boring machine. The disadvantages are: construction-related disruptions, damage to the surroundings, and inconvenience for neighbouring residents and traffic. After all, this method often requires that waterways and roads are diverted temporarily. The cut & cover method was used for the Velser Tunnel, the Schiphol Tunnel and various aqueducts.