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The Rimutaka Tunnel is a railway tunnel through New Zealand's Rimutaka Ranges, between Maymorn, near Upper Hutt, and Featherston, on the Wairarapa Line.

Contents 1 Length 2 History 3 Design 4 Traction 4.1 Diesel-Electric 4.2 Steam 4.3 Electric 5 Use of the tunnel 5.1 Passenger 5.2 Freight 6 References

The tunnel is 8.798 kilometres (5.467 miles) long, the second-longest tunnel in New Zealand, and allegedly, the Southern Hemisphere. It is the longest tunnel in New Zealand with scheduled passenger trains.

The tunnel was built to replace the costly Rimutaka Incline and its Fell engines, and the first shot was fired in 1948. It opened on 3 November 1955, five days after the incline closed. It was the longest tunnel in New Zealand, superseding the Otira Tunnel in the South Island, but in 1978 the Kaimai Tunnel (8.88 km, 5.55 miles) near Tauranga opened.

The Rimutaka deviation's ruling grade is 1 in 70, compensated for curvature. The tunnel itself rises at 1 in 400 from the western portal to the highest point on the deviation, roughly halfway through the tunnel, and then descends to the eastern portal at 1 in 180.^[1] It has a vent halfway through for ventilation, reaching the surface on the Rimutaka Rail Trail near the former route's Pakuratahi Tunnel.

The first locomotives to work through the tunnel were the 792 kW DG class - the tunnel was too long for steam locomotives, making the Wairarapa Line the first fully dieselised line in New Zealand. Today, DBR, DC and DX class locomotives run the route.

The annual Daffodil Carnival steam train from Wellington to Carterton has to be hauled by diesel-electrics attached to the front of the steam locomotive between Upper Hutt and Featherston, through the tunnel.

There have been proposals to electrify the tunnel and the Wairarapa line as far north as Masterton as an extension of the Wellington suburban electrification. The tunnel was designed to enable catenary to be installed but this has not happened, and the catenary finishes just north of Upper Hutt station.

Tranz Metro operates passenger services from Wellington through the tunnel to Masterton five times a day each way Monday to Thursday, six on Friday, and twice a day each way on Saturday, Sunday, and public holidays. Excursion trains also go through the tunnel.

The tunnel is used by some Wellington to Napier freight trains, and for freight from the Wairarapa to Wellington, notably wood products from the Juken Nissho timber mill at Waingawa, just south of Masterton.