The four Hex River Tunnels consist of a twin tunnel of and three single tunnels of , and , on the Hexton railway route between De Doorns and Kleinstraat through the Hex River Mountains of the Western Cape Province, South Africa. The line, which connects De Doorns in the Hex River valley with Touws River in the Great Karoo, is part of the main rail route between Cape Town and Johannesburg. Of the of track, are underground. Construction of the line eliminated the bottleneck of the Hex River rail pass.
The Hex River rail pass
The enormous Cape Fold Belt effectively separated Cape Town on the coast from the hinterland of Southern Africa, and had obstructed previous attempts to expand the Cape Colony's railway infrastructure inland. In 1872 the Cape Government, under Prime Minister John Molteno, ordered that a railway line must be constructed across this barrier in the vicinity of the Hex River Mountains. The Cape Government Railways (CGR) was formed and railway engineer William George Brounger was appointed to oversee the task.
Route
The Hex River Mountain was a major obstacle to be overcome during the construction of the railway between Cape Town and the diamond fields at Kimberley in the Northern Cape. In 1874 surveyor Wells Hood, under the instruction of Brounger, found a potential route up the climb from De Doorns in the Hex River valley to the top of the Karoo plateau east of the Valley, that would require gradients of no more than 1 in 40 uncompensated, very steep by railway standards, and tight curves with a minimum radius of . He also proposed that a short tunnel would be required.
By 1876, the Molteno Government had selected Thomas Brounger's proposed route through the Hex River valley, with the line to follow the route from Worcester through De Doorns, then along Hood's proposed pass across the mountain via Osplaas to the summit at Matroosberg, and then via Kleinstraat to Touws River.
Cape Gauge
The original line between Cape Town and Wellington was laid to standard gauge, but this gauge could not be accommodated economically on the tight curves required by the proposed Hex River rail pass. This led to a decision by the CGR to use a narrower gauge of across the pass. After initially making use of dual gauge, it was decided in 1873 to convert all existing trackage of the CGR to this narrower gauge that was eventually to become known throughout Africa as Cape gauge. Credit for the fact that most of the present day railway lines in Africa are Cape gauge can therefore be directly attributed to the Hex River rail pass.
First Tunnel
The original tunnel, Southern Africa's first railway tunnel, is situated at from De Doorns on the original line to Matroosberg. The tunnel is straight and the portals are of dressed stone masonry, but the inside is unlined. On the route ascending the mountain, Osplaas provided the only level stretch that was long enough for a conventional passing loop.
Progress of the building of the line: Reached Worcester, 16 June 1876, and by the end of 1977 had reached Montagu Road, now known as Touws River – thus past the tunnel.
Second Tunnel
This first tunnel served the railways for 53 years, until the track was re-laid in 1929 to diminish a curve to accommodate larger locomotives. In the process a new concrete lined curved tunnel was sunk alongside the original. Since another crossing place had also become necessary, a siding named Tunnel was fashioned just east of the tunnel by laying two level dead-end spur tracks that branched directly off on opposite sides of the main line. This allowed trains to wait in one or the other of these sidings to allow an opposing train to pass. This latter tunnel remained in use for sixty years, until the line across the pass was closed to rail traffic in 1989.
Despite its quick and relatively cheap construction, the Hex River rail pass served the South African Railways (SAR) for more than a century. It was the starting point of the country's first railway line to the Witwatersrand and opened the way for Cecil Rhodes' colonisation thrust into central Southern Africa.
Current route
The railway line between Cape Town and Beaufort West has a ruling grade of 1 in 66 and a minimum curvature of , except for the pass where the steep gradient and sharp curves restricted train lengths and required additional locomotive power to bank trains on the ascent. In 1943 the gradients between De Doorns and Matroosberg stations were eased to 1 in 40 compensated, while the curves were eased to a minimum radius of , but despite this the Hex River rail pass still formed a bottleneck that would require more drastic measures to be eliminated.