The Picton loop railway line is a partly disused railway line between Picton and Mittagong in the Southern Highlands region of New South Wales, Australia. The line consists of the original alignment of the Main South line prior to its replacement with a deviation along more gentle grades to the east. CityRail, the passenger rail brand of RailCorp, operates a coach service in lieu of the former passenger rail service. Six services are provided in each direction on weekdays.
The coach route serves the following stops:
The original lines, while gently curved, had gradients as steep as 1 in 30, which created a bottleneck as traffic increased. Picton became a busy station with an engine depot for bank engines.
In 1919, the alignment was shifted to an alignment with 300 metre radius curves and much easier 1 in 75 grades. The old line and stations continued to be used for passenger services until 1978.
The New South Wales Rail Transport Museum, located in Thirlmere and accredited as a rail operator, currently leases and maintains a 14-km section of the line to run historic trains.