Ara Tūhono - Pūhoi to Wellsford - Road of National Significance
The purpose of this project is to improve State Highway 1 between Pūhoi and
Wellsford in the northern Auckland region.
Route Selection to Scheme Assessment for the ~40km extension of the Auckland
Motorway network, from the north of the Johnston Hill Tunnels at Pūhoi, to
The study area covered over 550km² of rugged hill forest and farm
land, with over 1,000km of route design produced and documented using 12d Model
software. The ‘Preferred Route’ for the section from Pūhoi to Warkworth was
later announced following public consultation.
GIS was required to identify potential routes, based on weighted constraints
e.g. Social, Economic, Environmental, and topography.
Some 30+ long listed routes were to have alignments created and earthworks
produced for comparative and multi-criteria analysis to be carried out.
Within the study area, 14 geological terrain systems were identified, with
highly varied characteristics and irregular boundaries. The design of any
earthworks in 12d Model needed to take into account the high variability of the
geology along the route, as well as with depth of cut/fill.
The process needed to be robust, flexible and consistent across all routes
identified, and fast, given the length of each route and quantity to be assessed
over a short project time frame.
Decisional Templates were the obvious/traditional tool to use to cater for the
varied batter profiles given the depth of the alignment from the existing
These were then taken one step
further and given a form of spatial awareness so batter profiles could be suited
to the varied geological terrain systems encountered along the alignment, taking
away the need for designer intervention at terrain system boundaries.
This drastically sped up the initial creation of alignments, and resultant fine
tuning to meet desired cut/fill ratios.
process of adding spatial awareness to the decisional template was largely
straightforward, albeit slightly abstract; the various terrain systems were
assigned elevations and triangulated to create a tin with various plateaus. This
was the basis of the spatial decision making, with all batter scenarios
contained within the one template and covering the entire route (excluding
overrides for structures where required).
The completed routes (including e.g. interchanges, tunnels, viaducts and MSE
embankments) were documented straight out of 12d Model to DWG format for
compliance with company QA, and to PDF for detailed engineering assessment where
required. Volumes were sent to Excel and into GIS using shape files for back
analysis of social/ environmental effects and potential land requirement.
Benefits of the project include reducing congestion during peak periods, as well
as improving economic development and tourism opportunities in Northland.
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