Meldon viaduct – the UK’s wrought iron trellis viaduct on Dartmoor

In 1874, the London and South Western Railway opened a new route from London to Plymouth as a rival to Brunel’s Great Western Railway. An iron trestle construction was employed to reduce windage on the structure, which was built close to Dartmoor’s highest elevation of 621m.

By Tim Smith*

WHEN the London and South Western Railway opened a new route from London to Plymouth in 1874 to rival Brunel’s Great Western Railway, they chose a route crossing the northern edge of the granite outcrop of Dartmoor. This contrasted with Brunel’s coastal route to the south of this high ground. One of the obstacles was the steep valley of the West Okement river. To cross this, LSWR’s engineer, William Robert Galbraith, designed a trestle viaduct spanning 163m with a maximum height of 43m.

The choice of an iron trestle construction for the piers rather than the usual arched stone construction was said to be to reduce windage on the structure built close to Dartmoor’s highest elevation of 621m. The viaduct initially carried a single track. Photographs show this to be an alarmingly spindly structure. Just four years later, a second line was added requiring the building of a second viaduct alongside the first, the two being braced together to improve stability. Both structures were of wrought iron with cast iron trusses forming triangles in a single plane, but the first was of a riveted construction and the latter a welded structure.

The viaduct carried through trains until 1968 when the line was closed. However, it was still in use as a ‘head shunt’ for the nearby Meldon quarry which had opened in 1894 to supply stone for track ballast throughout Southern Railway’s network, which took over LSWR in 1923. Threequarters of all Southern’s ballast came from the quarry amounting to 100kt/yr. The stone was the form of very hard ‘hornfels’ arising by the heating of sedimentary rock by volcanic action which metamorphosized it some 290 million years ago in the late Carboniferous period.

In 1996, the viaduct became part of the ‘Granite Way’ an 11-mile walking and cycle path between the towns of Okehampton and Lydford. A year later, the viaduct, Okehampton station and two miles of track between the two were sold to Devon County Council for a nominal £1 and a trust set up to maintain these structures. In 1970, the down line was replaced with a concrete platform for lorries to carry construction materials for the building of Meldon Dam, to create a reservoir.

The quarry closed in 2012 but the track from Exeter to the viaduct remained with occasional excursion trains between Exeter and Okehampton station. A heritage railway operated between Okehampton station as far as, but not onto, the viaduct, but this sadly closed in 2019.

In 2021, the line was surveyed for reinstatement for passenger traffic from Exeter to Okehampton station by Network Rail. 11 miles of single track were relaid laying 24,000 concrete sleepers and nearly 29,000 tonnes of stone ballast. An innovative track laying machine was used which simultaneously dropped the sleepers into position, laid the rails and clamped them to the sleepers. The line opened just a year later and, taking the name of the previous heritage railway, ‘The Dartmoor Line’ now offers an hourly service between

Exeter and Okehampton. The line is run by the revived Great Western Railway company, an ironic twist since it was originally built to compete with the original GWR for traffic from London to Plymouth and on into Cornwall.

Some 150 years after first opening the line, once again it is serving the local community. When the line reached Okehampton in 1874, it replaced an arduous journey of two days by stagecoach from London. First small industries appeared, an artificial ‘manure’ works, a boot and shoe factory, a cabinet-making firm and a draper. In 1894, the quarry opened employing a workforce of some 3000. Agricultural produce could be sent to London in a journey time of around six hours and tourists were attracted to walk the tors of Dartmoor.

When the line closed in 1968, the town of Okehampton and surrounding countryside had to rely on road transport to Exeter to the nearest railway. With the line re-opening, not only does the line once again offer excellent access to the northern edge of the moors, but is also a valuable commuter link to Exeter and further afield.�