Roughly speaking, the future transformation of the Hofplein viaduct is in two parts: the top and bottom sections. By the top we mean the roof of the viaduct, which is still in use by Randstadrail. The departure of Randstadrail in 2010 will not only enable the top to be given a new use as a public space, but from then on the bottom of the viaduct will also undergo a visible transformation. The majority of the arched spaces under the viaduct that are now boarded up and neglected will at the same time as the top be provided with a new glass front designed by Atelier Kempe Thill. They are one of the three firms that the Hofbogen project office invited in 2007 to submit a design vision for these new glass facades. The main criteria for this multiple brief were: transparency, suitability to the monumentality of the viaduct, and the possibility of installing the new fronts in the various parts of the Hofbogen. The design created by Kempe Thill amply fulfils these conditions and is also simple and stylish, and in addition unifies the Hofbogen. The purpose, in advance of the actual transformation of the viaduct, is to ‘test’ the new frontage design in two archways in what we are calling the ‘Trial Arches’ project. This will give an impression of what the viaduct will look like in several years’ time and gives the Hofbogen project office the opportunity to investigate the structural state of this early twentieth-century monument.