The Cronulla end of the Illawarra Line was one of the last to be electrified, but also one of the first to be electrified through to its terminus. However, despite some duplication of track in the 1980s, it was not until 2010 that the line was fully duplicated all the way between Sutherland and Cronulla Stations. This lifted the cap on the number of trains that could travel along what was previously a single track of rail.
In conjunction with improvements on the city end of the line, including the construction of the Eastern Suburbs Line (which moved Illawarra Line trains from the City Circle and sent them towards Bondi Junction instead) and then the completion of a turnback at the Bondi Junction Station terminus (increasing the capacity at that station from about a dozen trains per hour to 20 trains per hour), this allowed a significant increase in the total peak capacity of the line. As a result, it is now possible to easily run 20 trains per hour on the Eastern Suburbs/Illawarra Line.