Gauge
The first of the main line railways in Adelaide was built in 1856 between the city and the port, in the 1,600 mm (5 ft 3 in) broad gauge, after a change from 1,435 mm (4 ft 8 1⁄2 in) to maintain compatibility with New South Wales. The main line to Melbourne was opened after a bridge was built at Murray Bridge in 1886. It was the first railway line between colony capitals to not have a break-of-gauge. It was also the last of these to be converted to standard gauge in 1995.
Because the narrow gauge lines started out as isolated lines from independent ports at Port Wakefield, Port Pirie, Port Augusta, Port Lincoln, Beachport, Kingston SE and Wallaroo, the problem of the nascent break of gauge was not immediately apparent. When the broad and narrow systems finally met at Hamley Bridge, Terowie, Wolseley and Mount Gambier endless complaints started. There may have been even more breaks of gauge, as the original bridge at Murray Bridge was designed for narrow gauge. The narrow gauge line at Port Broughton on the Yorke Peninsula was never connected to the main system.
The lines on the Eyre Peninsula and throughout the mid north were built to 1,067 mm (3 ft 6 in) narrow gauge. Once the standard gauge from Port Pirie to Broken Hill was built, the narrow gauge from Terowie was converted to broad gauge to Peterborough, .With completion of the Broken Hill Port Pirie Line i.e.narrow to standard, it left a short section of naraow gauge between Peterborough and Terowie, this was converted to broad gauge and Peterborough became the change of gauge station for Broken Hill Adelaide express. The narrow gauge line was retained north from Peterborough to Quorn.
The main interstate links from Adelaide to Perth, Darwin, Melbourne, and Sydney are all of 1,435 mm (4 ft 8 1⁄2 in) standard gauge.
Read more about this topic: Rail Transport In South Australia