Ngauranga Gorge
The erection of the strengthened gantry. The work was completed during one night-time road closure to minimise disruption to motorists.
(click to enlarge)
Rear view of variable message sign
Challenges
This project involved a number of complexities and challenges including a very tight timeframe for design, construction, testing and commissioning (approximately 15 months).
The Ngauranga ATMS was a pilot project. No off-the-shelf products were available to meet Transit's requirements, new technology had to be developed and tested.
The physical working environment of Ngauranga Gorge: steep terrain and extremely high winds provided challenging conditions for the design engineers. The variable message signs in particular are large and heavy and required specially strengthened support structures to ensure they would withstand the very high wind loading. The impact of wind and traffic vibration also had to be minimised to ensure that the pole-mounted cameras could accurately detect incidents. The 12m-high camera poles were designed to achieve a maximum tolerance of +/-10mm movement at a wind speed of 100km/h. Innovative structural designs were required to address these needs.
The lack of a fibre optic network in the Gorge meant that a mix of microwave, radio and cable technology was required to transmit information. This approach also minimised the quantity of trenching and cable placement, reducing the disruption to motorists during construction.
The high speed and high volume of traffic required careful attention to contractors' safety during the installation of the support structures (particularly the massive 36m gantry structure), fibre optic cable and radio antennas.
More than 100 road closures were required in the construction phase. They had to be carefully planned and managed to minimise delays, avoid accidents and brief the emergency services.
