Old tunnel retired after quake damage

it up to modern standards, which would cause considerable disruption. ‘‘Its small size means trains must slow down to go through it, which lengthens journey times on the line and causes operational constraints,’’ Gordon said.

The main north line and State Highway between Christchurch and Picton were critical elements of New Zealand’s land transport networks.

‘‘Bypassing the tunnel, which runs below SH1, allows us to improve rail operations and seismic resilience for both road and rail,’’ he said.

The small and curved tunnel was a safety risk for fast moving trains as they had to slow down to 25kmh to go through the tunnel. Once work is finished, trains will be able to travel up to 80kmh through the area.

The Tar Barrel tunnel (Tunnel 21) was built in 1913. The 167-metre-long tunnel is the oldest on the main north line.

‘‘Currently, about 36 train services travel along this section of the main north line each week,’’ Gordon said. The new alignment involves moving 1km of track through a cutting that required about 500,000 cubic metres of earth to be moved.

A new road overpass will be built over the railway south of the tunnel. Vehicles will be moved on to a temporary diversion at the

site this week to allow for the continued two-way traffic on SH1 through the area while the overpass is built. The dirt will be later used for landscaping purposes at the site, with native plants planned across 2 hectares.

‘‘The programme will cost slightly over $35m with currently 60 people working on site, and that will increase to 80 people,’’ Gordon said.

There were ‘‘up to seven excavators, four compactors, three bulldozers, six dump trucks, one piling drill rig, one crane and traffic control equipment’’ being used on the site, he said.

The Picton to Christchurch 335km train trip includes 22 tunnels and 175 bridges.

Last November, Prime Minister Jacinda Ardern announced Kiwirail’s Coastal Pacific passenger service would get a $40m investment and would become a year-round service.