The big push that’s helping make our motorway smart

The project to build New Zealand’s first ever smart motorway in Wellington is about to reach a significant milestone with the second and final push of an old off-ramp at Kaiwharawhara due next week, says the NZ Transport Agency.

Just out of sight under Wellington’s urban motorway, a significant engineering achievement has quietly been taking place for the last few months. While people driving along the motorway each day will be only too aware of the project’s replacement of the central median safety barrier, few will have noticed what’s been going on under the Thorndon Overbridge.

An un-used off-ramp (initially designed to access Ngaio Gorge from the motorway) is being re-purposed as part of a new northbound lane running from the Aotea on-ramp to the Ngauranga Interchange. The 300 tonne, two-span off-ramp has been lowered and is being pushed closer to the main Thorndon Overbridge structure.

Transport Agency project manager Glen Prince says it’s a very challenging task to move such large structures but one that’s saving money, reducing wastage and minimising disruption to road users.

“The alternative was to demolish the off-ramp and build a whole new bridge extension, so this innovation is a much better option.”

The newly-positioned off-ramp will then be connected to the Thorndon Overbridge. Thousands of steel reinforcing bars have already been inserted into the off-ramp and the overbridge. Concrete will be poured into the gap to ‘stitch’ the structures together.

“The stitch operation is planned for overnight on Saturday 1 August. Once poured, the concrete ‘stitch’ will be covered and heated to speed the curing process. We need to close the northbound lanes of the Thorndon Overbridge for up to 12 hours to reduce vibration and help the concrete successfully cure,” said Mr Prince.

“Also during the 1 August closure, we’ll erect two new cross-motorway gantries that are putting the smarts into our motorway. So the southbound lanes will also be closed for up to three hours.”

Detours will be in place and an information campaign will run in the weeks leading up to the closure. Other overnight closures (eight in total) will follow in August as more overhead gantries are manoeuvred into place.

Wellington’s smart motorway is being built between Johnsonville and the Terrace Tunnel. When it’s operational, early in 2016, it’ll make travel times more predictable during peak times and free up nearby roads for better public transport trips and improved amenity for pedestrian and cyclists. It will also provide an extra northbound lane between Aotea Quay and Ngauranga, which will be incorporated into the existing motorway ‘footprint’.


Check out our website for more information about the upcoming motorway closures and to see photographs and a time-lapse sequence about moving the off-ramp: link)