is now closed. The rest of the line was replaced in 1968 by a new route to the east of the new Forrestfield Marshalling Yard. Kewdale–Kwinana and the East–West Australia rail corridor Prior to the 1960s, the majority of railways constructed in Western Australia were built at narrow gauge, with the exception of the standard gauge Trans-Australian Railway linking Western Australia with South Australia at Kalgoorlie. In 1961 the Western Australian Government passed the Railways (Standard Gauge) Construction Act 1961 to construct a standard gauge railway between Perth and Kalgoorlie to facilitate the movement of interstate freight. The following new railways were constructed and existing railways upgraded to dual gauge, with construction complete by 3 August 1968 The Midland Junction–Kewdale line was converted to dual gauge and then rerouted around the new Forrestfield Marshalling Yard. A new Kewdale–Kwinana line was constructed between Kewdale and the Spearwood–Cockburn Cement line at Cockburn, and the Cockburn Cement line extended south to intersect with the Robbs Jetty–Kwinana line at Naval Base. A marshalling yard was constructed south of Rockingham Road. The Spearwood–Cockburn Cement line and Robbs Jetty–Spearwood line was converted to dual gauge, and continued north to Fremantle and the marshalling yards at Leighton. The Robbs Jetty–Coogee line to Woodman Point (now removed) was converted to dual gauge. The Kwinana loop rail was constructed at dual gauge. The railways constructed and upgraded under the Railways (Standard Gauge) Construction Act 1961 form the backbone of the freight railway network in Perth. Kwinana Loop The Kwinana Loop Railway is railway branching from the main line at Kwinana first constructed under the Industrial Lands (Kwinana) Railway Act 1966 and later extended to the CBH Group terminal under the Kwinana Loop Railway Act 1968 with a balloon loop at the terminus. The southern portion has not been constructed, and access to the Loop Railway is reliant upon the triangle intersection at Kwinana. The Department of Transport has identified the Kwinana triangle is now approaching capacity, and it is seeking alternatives in order to ensure that future growth in rail-hauled freight can be accommodated. Completion of the southern portion of the Kwinana Loop as planned, between the CBH balloon loop and the Kwinana–Mundijong line, is an option being considered. In December 2015 the City of Rockingham publicised its objection to the reinstatement of the extension of the loop railway. Kwinana–Mundijong The Kwinana–Mundijong line was constructed to connect Kwinana with