Between Amsterdam and Schiphol, and around Rotterdam, high speed trains operate on the existing line.

South of Schiphol the dedicated high speed tracks begin, parallelling the existing railway line until Nieuw-Vennep. The line then branches off eastwards, continuing along the west side of Roelofarendsveen and Hoogmade and entering a tunnel east of Leiderdorp. This tunnel was built to protect the character of the Groene Hart region. North of Zoetermeer the train line leaves the tunnel west of Hazerswoude-Dorp; it subsequently passes to the east of Benthuizen, and on an elevated track east of Zoetermeer, then back on the surface between Berkel en Rodenrijs and Bergschenhoek, and after a tunnel, joins the existing line again north of Rotterdam.

Trains run briefly on existing tracks for a few kilometres before entering the high speed line again. At Barendrecht the two tracks cross each other and the trains begin left-hand running as in Belgium, France and the United Kingdom. From here the line runs next to the existing railway as well as theBetuweroute, continuing through the Hoekse Waard area, bypassing Dordrecht. South of Dordrecht, the line runs next to the A16 motorway with a branch spurring off to the city of Breda. South of Breda, the line again follows the motorway towards Antwerp in northern Belgium. At the Belgian border, it connects to HSL 4, which carries on to Antwerp, with an existing line from Antwerp to Brussels.