In developing the SNRP designs, consideration has been given to the following road design principles, which have been selected based on reference to the AustRoads, Geometric Design guide:
- Limiting vertical grades to no more than 4%
- Limiting the horizontal radii of tunnels to not less than 300m
- Limiting the horizontal radii of viaducts to not less than 250m
- Positioning demerge points at least 200m from other demerge points in the same direction of travel to minimise weaving issues
- Positioning merging points at least 500m before subsequent merge point.
Borehole logs that have been prepared for LMA for the Reference Design and other alternatives have been reviewed to determine the location and depth of the underlying mudstone and Coode Island Silt that is present in the western end of the project. This information was used to determine how far a bored tunnel could extend and where cut and cover tunnelling techniques would be necessary.
Noise impacts to residential areas have been considered and noise prevention structures have been proposed where it is considered to be obvious that such structures will be required. However, the determination of what structures need to be constructed where to achieve the required performance requirements will need to be completed as part of the final design.
The LMA has nominated a large area of Royal Park for the Reference Design for lay-down areas and other construction requirements. For the alternative design, it is expected that the site of the urban renewal would be suitable for this purpose during construction. This land would then be able to be subdivided and sold after the completion of the link.
For both of the SNRP design alternatives, it is proposed that the performance requirements specify that the viaducts/tunnels connecting to CityLink at the western end be constructed and commissioned prior to the commencement of the tunnel. This will ensure that trucks carrying spoil will be able to be exported from the tunnel portal without having to travel through the local streets.