The Vale of Neath Railway was a broad gauge line that included a number of timber viaducts. For their design, Brunel mainly used the fan style, in which the main timber members conduct deck loads directly to the piers using converging straight members. As with the South Wales Railway, he confidently specified timber viaducts for suitable crossings, notably at Neath and Aberdulais.

The main members of the viaducts were typically of 305mm square section yellow pine. Up to five of these members might converge in a specially shaped cast iron shoe placed on top of a brick or stone pier. It was said that a good repair gang could renew any element in an hour, and that the timber could be expected to last 30 years.

At the town of Neath, the Vale of Neath Railway shared a station with the South Wales Railway. The first and longest timber viaduct on the Neath line, extended from the junction between the two railways. It was a fan-style viaduct, 247m long.

Proceeding north east up the valley, the next station is at Aberdulais. Here the railway crosses the River Neath again, alongside the 104m long canal aqueduct built by George Tennant (1765-1832).

The Dare Viaduct (or Dare Valley Viaduct, or Cwmdare Viaduct) was at Aberdare on an 1857 branch line into the Aman valley. It was 137m long and 21.3m high, and also of the fan type. The branch line closed to traffic on 1st September 1939. However, the viaduct remained in place until it was demolished in 1947, after a life of 92 years. The Dare and Gamlyn (see below) viaducts were the last complete examples of Brunel's famous timber structures to remain in active use. The masonry piers for both can still be seen.

Also on the Dare and Aman branch line of the Vale of Neath Railway was the Gamlyn Viaduct, at Penywaun in the Cynon Valley. It was 183m long, 21.3m high and of the fan type. It was demolished along with the Dare Viaduct in 1947, leaving only its masonry piers.

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