fast rail and electrification of the lines to Melton and Wyndham Vale will occur alongside planning for the Airport rail link, with construction set to start by 2022. Infrastructure Railway The rail network within the Melbourne metropolitan area includes dedicated passenger lines, dedicated freight lines, and lines shared by the two types of traffic. Nearly all passenger traffic and some intrastate freight operates on , while all interstate freight traffic operates on . Most suburban passenger lines operated by the metropolitan rail franchisee, currently Metro Trains Melbourne, are electrified with 1500 V DC overhead catenary. Many of the suburban lines share tracks with regional passenger trains operated by V/Line, and some V/Line services provide "peri-urban" service to areas of Melbourne not reached by the electrified network. Metro also operates an isolated section of unelectrified passenger line between Frankston and Stony Point. The network is centred on Flinders Street and Southern Cross stations in the CBD, which are joined directly by a six-track viaduct and indirectly by the underground four-track City Loop. From this central core, nearly all tracks pass through the three major junction stations of North Melbourne, Jolimont, and Richmond; and from there extend outwards to the west, north-east and east of the city respectively. There are few connections between the radial lines outside of the central city. Capital investment in the network since 1990 has focused on relieving "bottlenecks" near the central core caused by the large number of lines converging, most significantly with the Regional Rail Link project which provided additional capacity between Sunshine and the city. Much of the metropolitan network is double track or multiple pairs of tracks. There are small sections of triple track, which are used to allow express trains to overtake stopping trains in peak hour. Nearly the entirety of the Altona and Stony Point branches are single track, and many of the outer suburban passenger lines also have sections of single track, usually where demand for frequent services is low. The metropolitan network has a large number of level crossings. Many have been gradually removed by grade separating road and rail traffic: by 2016, some 228 grade separations had been undertaken in the Melbourne area, leaving 170 level crossings, although very few projects of this nature had been undertaken in the latter half of the 20th century. The Level Crossing Removal Project, which began in 2014, aimed to increase the rate