Road over railway Bridge, Ballinderry Road, Lisburn, Co Antrim, BT 28

Road over Railway Bridge, Ballinderry Road

This road-over-railway bridge at Knockmore, dating from around 1910, carries the Ballinderry Road across the main Belfast-Dublin railway line. It is a four-arch structure of considerable architectural and historical significance, built in brick and stone with concrete details typical of early 20th-century railway engineering.

The bridge is acutely skewed in its alignment, running northwest-southeast across the railway. Its four arches serve different purposes: the arch at the northwest end originally spanned the now disused Lisburn-Antrim line and only began to carry an actual railway after 1974; the second arch carries the 'down' line from Dublin to Belfast; the third carries the 'up' line from Belfast to Dublin; and the fourth arch at the southeast end was never used and is blocked at both ends by a galvanised steel fence.

The abutments are constructed of roughly-faced random sandstone blocks laid to courses, with tooled quoins topped with concrete. Detailed pilasters form buttresses at both ends, rising to out-projecting piers at the parapet ends. These piers are of red brick with cement-rendered concrete ends, each containing a semicircular arched opening to facilitate access between the arches. The arch soffits display skewly laid purple brick with four soldier courses forming the voussoirs, demonstrating skilful execution of skewed arches. The spandrels are of roughly-faced random sandstone blocks with a rusticated and margined sandstone string course running over and around the parapet terminal piers.

Angled wing walls of roughly-dressed random sandstone blocks are coped with purple brick having rounded edges. The parapets are of red brick, rising to a height of at least 1.8 metres, with their road-facing surfaces cement-rendered. The original purple brick copings survive along the northeast side, though these have been replaced with concrete on the opposite side. Terminal piers are capped with cast concrete. The approaches are ramped at both ends. The curved deck carries two lanes of traffic and a footpath.

The bridge's distinctive four-arch design reflects the Great Northern Railway's unrealised intention to provide four separate tracks along this section of line. Built to replace an existing level crossing (shown on 1857 and 1900 Ordnance Survey maps), the bridge first appears on the 1921 map. The four arches were likely conceived to allow stopping trains to use the outer arches whilst non-stop passenger and goods traffic used the inner arches. A third track had been constructed in 1907-08 from Belfast to Balmoral, and in anticipation of further expansion, both this bridge and that at Finaghy were built with extra arches. These additional lines were never laid, however, due to the First World War and its aftermath, leaving the outer arches unused for most of the bridge's life.

The railway line itself—the Lisburn-Lurgan section of the Belfast-Dublin railway—was opened by the Ulster Railway in 1841. The bridge was constructed during the Great Northern Railway period (which operated the line from 1876). West of the Ballinderry Road at Knockmore Junction, lines diverged north to Antrim and south to Castlewellan. The Castlewellan branch closed in 1956 and the Antrim line in 1960; the junction itself closed in 1960.

In 1974, Northern Ireland Railways reopened the line between Lisburn and Antrim as a dedicated single-track, which for the first time caused the northwestern arch to actually carry a railway. Knockmore Station opened at the same time, with platforms at both the southwest and northeast ends of the bridge. The station operated until 2005 when passenger demand declined following closure of the line in 2003. Although the Antrim line is now defunct, track remains in place.

The bridge is of particular interest as the only unaltered road-over-rail bridge with four arches in Northern Ireland—the other example at Finaghy has been recently widened. Its acutely skewed brick arches represent a particularly good structural example of their type. The regularity of the arches, combined with the use of red and purple brick with sandstone dressings, gives the structure architectural distinction. The extensive use of brick for the arches, piers and parapets, together with non-structural concrete applied only to pier ends and abutment quoin copings, is characteristic of early 20th-century bridge design. The structure is also of industrial archaeological interest and local historical importance in reflecting the growing volume of traffic along both road and railway during the early decades of the 20th century, which necessitated replacement of the level crossing.