A modest but particularly interesting goods traffic was operating on a section of the BCDR system around 1905 - fish from Ardglass was being transported by rail to Belfast via Downpatrick. The single-track line from Ardglass to Downpatrick, measuring 7¾ miles in length, had been constructed between 1890 and 1892 as one of the "Balfour" lines under the Light Railways (Ireland) Act 1889. Various estimates had been made regarding the cost of construction. The original proposal was for a narrow-gauge line costing approximately £50,000, with the Treasury contributing a free grant of £30,000 and the County guaranteeing interest at 3% per annum on £17,000. The Belfast and County Down Railway Company was to supply the remaining capital and oversee the construction of the extension. On 29 November 1890, the construction of the Downpatrick, Killough and Ardglass Railway by the BCDR was officially sanctioned through an Order in Council, and work was set to begin immediately. After careful deliberation, the BCDR directors opted to build the line to standard gauge: However, this decision meant that the additional cost of constructing a standard gauge line, as opposed to narrow gauge, had to be borne by the railway company. The Allport Commission of 1888 had estimated the cost of a standard gauge line—of which they were strongly in favour at approximately £38,000, or £4,900 per mile. In reality, the engineering works exceeded £60,000 (equivalent to approximately £8.24 million in 2023). The BCDR not only contributed a significant portion of this amount but also provided all locomotives, rolling stock, and terminal facilities. The £17,000 in baronial guaranteed shares were issued at 88, yielding £14,960. Combined with the Treasury grant of £30,000, this still left over £15,000 to be covered by the railway company. The total construction cost included £7,550 for working stock and an extension to the harbour at Ardglass, bringing the total length of the line to 8 miles and 4 chains. The entire route was built to standard gauge, with rails weighing 80 pounds per yard. At the time of the Downpatrick–Ardglass line’s construction, a loop line was also built across the marshes in the
Quoile estuary, about a mile southwest of Downpatrick. This allowed through trains between Belfast and Newcastle to bypass the county town for the first time since the completion of the main line in 1869. ==Gallery==