It's an ongoing process, keeping a major highway safe and fast in this challenging place. This is the stunning Otira Viaduct, opened in 2000. It wasn't here last time Pip came this way in 1998; she took the old, infamous Zig Zag highway which corkscrewed along the edge of the cliff. It was deemed dangerous and unsustainable, and the decision taken to create this bridge. (Construction must have already started when she drove through.)
It is particularly interesting because not only is the sheer engineering pretty awesome, but this is an area of immense conservation and cultural value. Transit NZ worked with the Department of Conservation and tangata whenua (people of the land, the Maori) in the decision on whether to build the viaduct (compared to, for example, a tunnel) and then in the design and construction process. Thus, for instance, the areas of the surrounding National Park such as the old road were replanted with native species grown from seed collected locally.
It cost a lot of money of course, but it was deemed essential to maintain this central highway. It can still be closed by heavy snow, or made pretty exciting in high winds, but it has enormously high resistance to seismic disturbance and rock-fall deflectors on the four piers. Pretty impressive.
We are parked for the night at Avalanche Creek DOC site, essentially a car park opposite the Visitor Centre in Arthur's Pass township. We bought some splendid sausages at the Blackball butchers (just outside Stillwater); tonight it's the garlic venison and beef with cauli mash and beans. Warming in all this rain. But - hooray! There are no sandflies.