An installation is very much dependent on the site specific layout and ground topography.
Where one verge is higher, the entrance units should preferably be laid in the higher verge with a fall of 1% towards the carriageway.
The tunnel in the carriageway should be appropriate for the camber of the road, with a fall of at least 1% and the chosen depth of cover. Where solid top units are used then the tunnel may also be laid with a zero fall or a continuous fall.
The entrance in the lower verge should be laid with a fall of up to 12% in order to allow swift clearance of water from the tunnel.
It is essential that no low point is created anywhere within the length of the tunnel and entrances in order to prevent localised flooding or standing water.