Auld's Bridge, Three Mile Water Park, Hawthorne Road, Newtownabbey, Co Antrim

Auld's Bridge is a single-span railway bridge constructed in 1933 from reinforced concrete, now located within Three Mile Water Park at Hawthorne Road, Newtownabbey. The bridge was built by the London, Midland and Scottish Railway Company (Northern Counties Committee) as part of the Greenisland Loop scheme, which connected Whiteabbey on the Belfast-Carrickfergus line with Monkstown on the Belfast-Antrim line. The loop opened in 1934 and eliminated the need for Antrim-bound trains to reverse at Greencastle, shortening the journey by approximately 2.5 miles.

The bridge displays modern architectural character influenced by International style, with clean lines and a notable use of mass reinforced concrete rather than concrete framing, which was unusual for this particular railway line. It is constructed using in-situ concrete with textures created by different formworks. The structure features a segmental-headed arch with a chamfered formwork line above creating a surround. The bridge is dated 1933 on a raised keystone section on each elevation. The smooth concrete elevations and lined soffits are typical of the period's technical approach. Piers are splayed to the base. The carriageway is approximately 6 metres wide with no parapet; a modern steel handrail has been added to the elevations.

The Greenisland Loop scheme has been described as "one of the most significant examples of modern railway architecture in the British Isles" and was directed by the NCC's resident engineer W.K. Wallace. Several other reinforced-concrete bridges were erected in connection with the scheme, including those at Bleach Green Junction (1931-33), Jordanstown Road (1931), Jennings Park (1931), and Mossley (1933). The loop line remained in regular passenger service until 1976 when Belfast's Central Railway opened, after which Antrim-bound trains were re-routed via Lisburn and Crumlin. The line remains in periodic use for goods trains. The bridge is set within the public park with the Main Road running parallel to the railway to the north.