During the Industrial Revolution, and the mass-extraction of coal from South Wales, there was a resultant growth in construction of railways into the South Wales Coalfield. The Taff Vale Railway so monopolised the trade of shipping coal to Cardiff Docks, that mine owners were desperate for competitor railway companies to both improve speeds of shipping, provide access to new markets, and hence reduce shipping rates. The London and North Western Railway had developed a route for the industrialised West Midlands and Northwest England, by controlling the Llanfihangel Railway and the Grosmont Railway's as feeder lines into the Hereford Railway, and hence onwards via the joint GWR/LNWR controlled Shrewsbury and Hereford Railway. This allowed shipment of goods from Pontypool and the Ebbw Valley to Hereford. However, access to the productive Rhymney Valley and Rhondda Valley coalfields was at best restricted, through having to route trains south to Cardiff along the TVR, then along the South Wales Railway to Newport via the GWR, before being able to access LNWR controlled track. The UK Parliament hence approved an Act of Parliament on 3 August 1846, the construction of the Taff Vale Extension, which would connect Coedygric North Junction at Pontypool with the TVR/GWR at Quakers Yard, and hence allow direct and LNWR controlled access. The LNWR approved the required capital expenditure, and merged the existing three railways and the extension project in the new Newport, Abergavenny and Hereford Railway.
Construction
The route for the Taff Vale Extension required the construction of two significant viaducts across two major river valleys: one across the Ebbw River, and one further west across the Rhymney River, the Hengoed Viaduct. This would be the last major project for the NA&HR to complete the Taff Vale Extension before the line was opened in 1858. Charles Liddell, the chief engineer of the NA&HR, decided that while a stone bridge would be impractical at Crumlin due to the narrow valley sides and hence high winds, at Maesycwmmer all of the natural resources existed to build an effective stone viaduct. Having won the contract to design and provide the structure of the wrought iron bridge at Crumlin, it was natural for the Scottish civil engineer Thomas W. Kennard to win the design of the Hengoed Viaduct. Apart from spanning the Rhymney river, the viaduct also had to span the Brecon and Merthyr Railway's station on the south side, and curve slightly across the valley to initially form a junction with the B&MR on its northern side, before entering the Bryn Tunnel. With a stipulated completion date of 1 October 1854, Liddell engaged contractors Messrs Rennie and Logan, who began work on the masonry structure in mid-1853. Maesycwmmer was a quiet rural farming valley before 1846, but the first project of Messrs Rennie and Logan was to construct both a quarry, from which to extract stone to build the viaduct, and also a complete housing and social complex to house the workers and their families. The houses remain along the present main road, while the now-disused quarry lies in a field behind the houses of St Anne's Gardens. Liddell's design consisted of 16 arches, with the first effectively a separate bridge skewed across the low level B&MR, to allow for crossing their Hengoed railway station. With a maximum height above the valley bottom of and a full length of, construction came at a cost of £20,000, with one fatal accident.
Operations
The line opened as a double track as agreed in 1858. Integrated as part of the Great Western Railway during the railway grouping in 1921, in 1928 the entire length of the Taff Vale Extension was downscaled to a single track. Through passenger and goods traffic ceased over the viaduct on 15 June 1964, and the line was completely closed and the track lifted later that year as part of the Beeching Axe. After the closure, Hengoed viaduct was offered for sale at a nominal sum of £1.
Today
Inaccessible to the public for over 35 years, it was agreed for the viaduct to become part of the National Cycle Network. Integrated as part of the Celtic Trail within National Cycle Route 47, which provides a traffic free cycle route from Quakers Yard to Newport, its ownership was transferred from British Rail to Railway Paths Ltdin 1999. Hengoed Viaduct was opened for public access in 2000. In April 2004, the Heritage Lottery Fund gave Caerphilly borough council a grant of £870,000. This allowed a programme of refurbishment to take place, including repairing and repointing to the pier bases, parapets and arches; as well as repairs to the remains of Hengoed ‘High Level’ Station at the western end of the viaduct. Works have improved public access and safety, with new fencing, viewing platforms and the installation of lighting. Finally, the site and route was added to by the addition of "Wheel o Drams" sculpture by Andy Hazell, an unusual piece of modern art formed from a circle of coalmining dram trucks to commemorate the industrial heritage of this locality within the history of the South Wales Valleys.
