The Illawarra lines are also connected at this point to the "Illawarra Relief Lines" which emerge from underground and lead to the Eastern Suburbs Line. From Illawarra Junction, four tracks head south through Erskineville and St Peters to Sydenham station. The 'main' pair of tracks are used by Eastern Suburbs & Illawarra Line and South Coast Line trains and the 'local' pair by Bankstown Line and peak hour Inner West & Leppingtonh Line trains. At Sydenham, the Bankstown railway line branches off, but trains from the Airport, Inner West & South Line continue along the Illawarra line until Wolli Creek, where a junction to the East Hills line exists. South of Wolli Creek station, a crossover allows trains from the 'main' pair of tracks to switch to the 'local' pair. This is used by peak hour all-stations Eastern Suburbs & Illawarra Line trains. The four track section ends at Hurstville. The line then continues as two tracks south towards Sutherland, crossing the Georges River via the Como railway bridge between Oatley and Como. At Sutherland the Cronulla line branches in an easterly direction. The main line then heads in a southerly direction, parallel to the Princes Highway to the west and bordering the Royal National Park on its eastern side until Waterfall, the last suburb in the Sydney metropolitan area. The track continues south from here as the South Coast Line through the Royal National Park towards the Illawarra region. The Illawarra line route was approved by the New South Wales Government in 1880. This route originated near the inner-city locality of Macdonaldtown and ran to Kiama via the locality of "Bottle Forest", a distance of . The route selected comprises the present-day route of the Macdonaldtown to Waterfall section of the Eastern Suburbs & Illawarra Line. On 6 April 1881, Governor Augustus Loftus assented to Act 44 Vic. No. 28, which provided £1,020,000 for the construction of this railway, and proposed that the first section of , constituting approximately the present suburban route, be completed by 30 September 1884. Almost immediately, concerns were raised about the new route's viability, most specifically over the cost of tunnelling between Waterfall and Otford to reach Wollongong. Work was suspended past the 24 kilometre point at Como, and Government surveyors were instructed to re-survey a route via the Port Hacking River that had originally been surveyed in 1873.