The viaduct crosses the A12 motorway, the railway line Utrecht-The Hague, and the greenhouse area. At 17.5-metre intervals the viaduct is supported by a row of three piers, which are placed in line with the direction of the viaduct/high-speed trains. The rail viaduct is 6 metres high on average. At the crossing with the bundled A12/railway line Utrecht-The Hague, the rail viaduct is around 10 metres high, and here it has 17 spans of 33.5 metres each. Here the viaduct is not supported by rows of three columns, but by two piers that are connected to each other by concrete beams. Thanks to its high construction and the large spans, (future) roads and waterways can be led under the HSL with minimal hindrance.

The rail viaduct is built on concrete piles. These are driven into the ground at the places where the piers support the viaduct. The number of piles depends on the type of soil and varies between 14 and 20. The length of the piles is between 8 and 14 metres; the longest pile is also the heaviest: 5 tons.

If necessary, steel sheetpiling is drilled into the ground around the piles to make a construction pit.

The ground inside the construction pit is excavated down to a few metres below surface level. If necessary, the groundwater level within the sheetpile walls will be reduced by means of draining. The groundwater level outside the pit is not lowered.

nAt the top of all the piles that have been driven into the ground, the concrete is hacked off over a height of 50 centimetres, thus freeing the reinforcement (interweaved steel bars).

Around the tops of the piles a construction floor is laid out. On this construction, the reinforcement for the base is made. The base is a concrete block of 12.5 x 4 x 1.5 metres. It is the base of the pier and serves to transfer the forces and loads from the viaduct via the piers to the concrete piles. Around the reinforcement the formwork for the base is put in place. At this stage, the reinforcement for the piers is already placed inside the reinforcement of the base. Then it is time to fill the formwork with concrete. The base now is anchored thoroughly to the piles, thanks to the interconnected reinforcement. In the same way, the pier is anchored to the base, because the pier's reinforcement is already installed when the base's concrete is poured. Now the concrete must harden for a certain period. After this, the formwork can be removed.

Around the reinforcement protruding from the base, reinforcement nets are put in place, which is then enclosed by special, steel formwork that is reusable. The formwork is built up in segments due to the varying height of the piers. Before the concrete can be poured, a number of provisions, such as rainwater drainage and earthing are installed. (Earthing is necessary to lead the leakage currents to the earth, to prevent the concrete from becoming affected and weaken the construction; see also 'The Line' > 'Power'.) 

Then concrete is poured in stages into the formwork. The workers have to consider the liquid pressure that occurs at the base of the pier when the concrete is being poured. If too much concrete is poured at once, there is a risk that the pier collapses. For this reason, no more than 2.5 cubic metres of concrete may be poured per hour. The piers vary in height and three piers in a row are filled with concrete at a time. The rows are at right angles with the direction of the train. While the concrete is poured, it is compacted with a vibrator needle, which whips the air out of the concrete, making the construction stronger. After two days, the concrete has hardened sufficiently and the formwork is removed.

The construction pit is closed again with earth to a level above the base, after which the sheetpiling is removed. From that moment on, the pier bases are no longer visible.

After hardening for 28 days, the concrete of the piers finally has reached its definitive strength. Now the decks that hold the rails can be put in place. The 163 decks of the viaduct north and south of the A12 motorway were built with an innovative formwork system. With a traditional construction method, it would take three to six weeks to build a single deck. Through the use of the innovative modular formwork, and by prefabricating the greatest part of the reinforcement nets in a separate location, it is possible to build one deck per week. An important feature of modular formwork is that it can be shifted without disassembling the entire formwork system. The 17 decks on the viaduct over the A12 consist of a row of prefabricated concrete joists, on top of which a mesh is made and concrete is poured in the traditional manner.

On the outside walls of the two parallel rail ducts, facilities are installed for the prefab side elements. At a later stage, the superstructure contractor will place sound barriers or fences on these side elements.