The line was built with economies that doomed it to inefficient operation. There were tight curves ( radius north of Clare), 1:60 grades, second-hand rails, and reinforced concrete bridges that were designed for light axle loading. When larger locomotives were introduced on the South Australian Railways in 1926, the Spalding line was unable to carry their greater weight. The motive power up to 1950 was mainly
Rx class engines, with the occasional
Q class and
S class. Commencing early 1951, the line was worked mainly by
750 class locomotives. From 1960 the line was worked by
830 class diesel-electric locomotives. There was a major bridge over the
Broughton River, just south of Spalding. It still stands, and in 1993 it was heritage listed. That listing was a consequence of the inclusion of the bridge in the 1985 book by Colin O'Connor "Spanning Two Centuries - Historic Bridges of Australia". O'Connor's book contains inaccuracies in relation to this bridge. It attributes its design to
Alexander Moncrieff, but the contract drawing is signed by Alex's brother Joseph. When the bridge was designed, Alex Moncrieff had not worked for the South Australian Railways for two years. Its 5-arch design was, by engineering standards, more than a decade obsolete when the contract was signed in 1918. Australia's expert on ferro-concrete construction,
John Monash, had abandoned that style of bridge by 1906. When the Broughton River bridge was completed in 1919 there was a dispute over payments to the contractor, Joseph Dixon. The matter went to the
High Court of Australia, which was critical of Joseph Moncrieff's handling of the contract, yet by a majority the High Court found in favour of the South Australian Railways. ==Safeworking==