The Rimutaka mountain range separating Wellington and the Wairarapa presented railway engineers with a difficult situation. Although a suitable alignment could be found on the western side of the range, on the eastern side surveys were less successful, the only practical route was that with graded steeper than that used with conventional railways. An average grade of 1 in 15 was used to descend a three-mile section of track between Summit and Cross Creek on the Wairarapa side of the range. The incline, part of the Kaitoke to Featherston section, was opened for traffic on 12 October 1878.
The patented Fell centre-rail system was employed to enable specially-fitted locomotives to negotiate the steep grade safely while hauling larger loads than otherwise would have been possible. Four Fell locomotives were initially built for the incline in 1875, built by the Avonside Engine Company. They were joined by a further two built by Neilson and Company in 1886. Traffic continued to grow, boosted by connection to the Napier-New Plymouth railway in 1897, later relieved to some extent by redirection to the route of the former Wellington and Manawatu Railway Company, purchased by the government in 1908. A few conventional locomotives were also used on the incline, including an experimental Mallet compound 'E' 66. After World War I the incline was principally worked by the six Fell locomotives.
Dramatic improvements in passenger service schedules were achieved from 1936 with a fleet of 6 railcars built at Hutt Workshops, known as the 'Wairarapa' railcars. The railcars were used for most passenger services until the incline closed, with the exception of special passenger trains and holiday traffic.
Near the end of its days the Rimutaka Incline bore witness to the passage of a Royal Train carrying HM Queen Elizabeth II and the Duke of Edinburgh. The train comprised four 56' carriages and a 56' van, which were test-hauled over the incline in December 1953, proving worthwhile as the Royal Saloon came into contact with one of the Incline tunnels. Some minor track adjustments put matters right. On 15 January 1954 the Royal train carried the Queen down the Rimutaka Incline en route from Wellington to Masterton, this time without any problems. Empty coaching stock was hauled up the incline later in the day, the Queen returning to Wellington by road (except for a brief re-embarkation at Kaitoke).
Immediately on departing Summit station yard the line entered the 630 yard (576 metre) Summit tunnel, piercing the Rimutaka Range 300' (90 metres) beneath the 1440' (440 metre) Rochfort Pass. A slight uphill gradient of 1 in 1000 was provided for 10 chains (200 metres) of the tunnel, whereupon the descent commenced, at 1 in 300 for 11 chains, rapidly steepening to a maximum of 1 in 15 shortly after exiting the tunnel.
Minimum radius curvature of 5 chains (100 metre) radius was used extensively in the descent to Cross Creek, the longest straight being a mere 8 chains (160 metres) long. Two further tunnels were bored, Siberia, 132 yards (120 metres) and Price's, 107 yards (98 metres) long. An impressive 5 chain radius curve commenced within the bore of Siberia tunnel, continuing through 144 degrees as it crossed Horseshoe Gully by lofty embankment. Siberia Curve, as it became known, was the site of a freak accident on Saturday 11th September 1880, in which four children died as a result - three at the scene and one later from his injuries. Two carriages that were propelled ahead of the Fell locomotive were blown off the line by a gale force gust of wind. Breakwinds were erected at Siberia curve and other locations on the incline, and near Pigeon Bush to protect trains from wind gusts. This was the only serious accident on the incline in 77 years of operation.
Public Works Department Wellington - Masterton Railway Summit Contract, 1875. National Archives Agency AATE Accession W3409 Folder 53 Part 9.
Public Works Department Wellington - Masterton Railway Incline Contract, 1875. National Archives Agency AATE Accession W3409 Folder 65 Part 46.
Cameron, W.N. 1992. 'Rimutaka Railway', New Zealand Railway and Locomotive Society, Wellington, New Zealand.
1 New Zealand Railways, Archives New Zealand / Te Whare Tohu Tohituhinga O Aoteaora: [Archives reference: AAVK W3493 B-5261]
2 New Zealand Railways, Archives New Zealand / Te Whare Tohu Tohituhinga O Aoteaora: [Archives reference: AAVK W3493 B-6407]