N206 Tjalmaweg, Katwijk - Leiden

Green road with Roman past

The provincial road N206 stretches from Leiden to the coast, cutting through the open landscape of the former military airbase Valkenburg and Katwijk. As part of the so-called Rijnland-route that connects the city with the A44 and the A4, there is a need to renovate and widen the road.

Adapted to the landscape

With a large residential extension planned at Valkenburg, the provincial authority considers it a high priority to ensure that the infrastructure is integrated as green as possible. The widened N206, the new bus lanes and the new high-speed bicycle paths have to be designed in a way that adapts to the landscape and causing as little harm as possible. The design that the architectural office ZJA and Bosch Slabbers landscape architects made for the N206 Tjalmaweg includes a number of innovative elements to make sure that those design considerations are met. These innovations do not only relate to adaptating to the landscape but also to sustainable methods of building and respect for the history of the landscape.

Building greener

A traditional highway lies on top of the landscape as a conspicuous plain of asphalt and concrete. The N206 Tjalmaweg is constructed below ground level over most of its length, hiding itself wherever it can. To avoid creating a drab concrete corridor the walls along the sunken road are overgrown with different species of climbing plants, in order to soften the road’s walls and make them greener. This is made possible by a construction technique with plastic foils and soil that is also used in the landscaping of parks. This method cuts down on the amount of concrete (and thereby reduces energy costs and CO⊂2 emissions) and creates space for the soil with the climbers that grow up against the walls.

A sophisticated planting scheme ensures a changing look in all seasons. The sunken N206 runs through a wide park zone, that also accommodates hiking paths, waterways and the new and improved bicycle paths, surrounded by trees and shrubbery.

To offer the plants a firm hold and to make sure that from the very start driving along the N206 offers a pleasant view, the walls are outfitted with slats made from a composite of resin and recycled textiles.


The history of the landscape

Two flyovers intersect the N206, at Valkenburg and by the Torenvliet bridge over the Old Rhine. Near one of the flyovers the design includes a resting place, right outside the bicycle underpass. At the border of a small lake, the bicycle path forks off and transforms into a reconstruction of a Roman military road. Gradually it changes into a clay path that disappears into the water. This marks the exact spot where archaeologists dug up remnants of the Roman frontier road, the so-called limes.

The spot, shielded from the highway, offers an opportunity to rest and contemplate the landscape and its history, with the help of the replica of a part of the Roman road and a sign with additional information. A construction made out of rough wooden beams can be used as playground equipment but is also a replica of the installation used by the Romans to hammer the cobblestones into the road’s surface. Into the slatted walls graphic elements will be placed that refer to the Roman presence in the area.

To recycle a bridge

Alongside the existing bridge at Torenvliet, a new much wider bridge is build. The existing bridge is a fifty-year-old bascule bridge that is not required to open in the new situation. Instead of demolishing the obsolete bascule basement building and removing it from the landscape, ZJA decided to maintain the building. The bascule basement, placed right in the middle of the canal, that used to house the contra weights, is a characteristic feature and offers an excellent opportunity to add some ecological value to the new Torenvliet bridge. In the design, the basement, sporting the coat of arms of the Province of South Holland, is destined to become a bat cave. From the bank of the canal a Batman sign will be beamed onto the wall to remind the people passing by of the bats.

Extra attention has been paid to what in jargon is called the underworld of the bridge. At the Torenvliet bridge this rather wide area will be designed and outfitted to make sure resting cyclists, anglers and hikers feel comfortable there and are inclined to loiter. This is done by the colour scheme, the construction of sitting elements and banks in the form of staircases. Another feature is the lay out of the parking spots, to avoid a tight pack of cars. The lighting provides a safe and clear atmosphere after sundown.


Nomination: Rijnlandse Architectuur Prijs 2023

Client: Provincie Zuid-Holland
Principal: Boskalis
Architect: ZJA
Landscape architect: Bosch Slabbers Landschapsarchitecten
Year: 2018 - 2023

Project: #992



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