ONLY half of Sydney's busiest peak-hour trains run on time when using a tougher measure of train delays, a leaked internal analysis by RailCorp shows.
The documents show just 46 per cent of trains run within two minutes of their timetable on CityRail's Western Line in the busiest hour of the morning.
The result is a far cry from RailCorp's published statistics showing more than 90 per cent of trains run on time, based on a more relaxed definition of trains arriving up to five minutes late.
The failure to achieve better on-time running can be annoying for commuters waiting for trains.
But in the peak hours, when trains are scheduled frequently, late-running trains prevent RailCorp from running extra trains needed to reduce Sydney's chronic overcrowding.
RailCorp's analysis of on-time running for the first three months of this year, obtained by the Herald, shows a gulf between the published statistics and an efficient network that allows the maximum number of trains to service the rush hour.
The figures show that during the 7.30am-8.30am peak hour for trains on the Western line, 90 per cent of trains run on time if based on a five-minute measure.
But on a three-minute measure the proportion drops to 66 per cent; on a two-minute measure it drops to 46 per cent; and on a one-minute measure it drops to 21 per cent.
Over the peak three-hour period in the morning, the figures are slightly better but well short of optimum levels.
RailCorp changed the definition of ''on-time-running'' from three minutes to five minutes when it slowed the timetable in 2005. The move was criticised by Barry O'Farrell, who is now Premier, saying the trains were only running on time because RailCorp had changed the benchmark.
Shortly before and after the Olympics in Sydney in 2000, the rail network reported 90 per cent on-time running using the old three-minute measure.
Now trains in the morning peak are already so crowded they make even the more relaxed five-minute definition difficult to achieve, because passengers take so long to board and alight.
The Herald reported last week Transport for NSW is preparing plans to radically simplify CityRail's train operating patterns to free up capacity on the Western Line, allowing more trains to run at crucial times.
The plans include running Richmond Line trains to Campbelltown instead of to the city and terminating Epping to the city trains via Strathfield at Central.
The idea behind the plans is to prevent trains from other rail lines joining the Western Line, which runs between Penrith, Blacktown, Parramatta and Central.
This would improve the capacity of the Western Line to run a reliable 20 trains or more an hour on the line but it would also force more commuters to change onto these services if they wanted to continue all the way through into the city.
Asked about the leaked internal analysis of on-time running, the Transport Minister, Gladys Berejiklian, said she knew customers wanted more frequent and reliable services.
''We are also working on a new timetable and it will be released at the end of 2013 with the aim of providing more express or semi-express services for customers travelling longer distances, including on the Western Line,'' she said.
''In addition to the overhaul of the timetable we are looking at better ways to provide customers with real-time information and other important measures like journey times.''
❏ The government began a trial of selling space for advertising on the side of CityRail trains at the weekend. Advertisements for Emirates are being displayed on the outside carriages of two Tangara trains.