But the Waratah trains, at one point 18 months delayed, are now the pride of the city's rail fleet, offering a much more reliable ride than any other train in Sydney.

Figures obtained via freedom of information laws show that last year the Waratahs made up about a quarter of the city's rail fleet but were responsible for only 5 per cent of the faults on trains in Sydney.

The results represent a remarkable turnaround for the Waratahs, which were ordered in 2006 in a project that soon became bedevilled by delays and cost over-runs.

The most unreliable trains in Sydney, according to the figures obtained by Fairfax Media, are the V-Sets. These trains travel through the Blue Mountains to Lithgow and on the northern line to Newcastle.

The V-Sets made up about 10 per cent of the city's rail fleet in 2013. But they were responsible for about 20 per cent of the faults in the fleet.

The problems captured by the freedom of information request include faults in doors, air-conditioning, brakes and lighting.

The performance of the Waratahs raises questions about why Transport Minister Gladys Berejiklian did not order more of them.

The final or 78th Waratah was delivered to the NSW government by manufacturer Downer EDI in May.

The government had an option to buy at least 20 more of the Waratah trains, which would have meant the entire Sydney rail fleet had air-conditioning.

Instead, Ms Berejiklian has said she will buy about 65 new trains "off-the-shelf" to use on long-distance lines to the central coast, Newcastle, the Blue Mountains, and the Illawarra.

The Minister expects these trains to arrive between 2019 and 2024 – a final delivery time almost as long as the delayed Waratah project.

Ross Spicer, the chief executive of Downer Rail, said the reliability figures represented a "very good result" for the Waratah Project.

"I have worked on about seven new train introductions in my career and this is the best-performing train we've ever put into service," Mr Spicer said.

He said the delay on the project had reduced to nine months after blowing out to 18 months at one stage.

One of the issues with the Waratah trains has been the large amount of electricity they need. This has meant the former RailCorp had to upgrade power supplies along the western line.

Mr Spicer said the main drain on the electricity was the air-conditioning, which adjusts depending on passenger numbers.

"It has got to work all the way up to 50 degrees and it balances to the number of people in them," he said of the air-conditioning.

The only trains in Sydney without air-conditioning are the S-Sets. These are soon scheduled to be used only as stand-by services, or to run on the T7 Olympic Park Line.

"The new intercity trains will replace both Oscars and V-Sets for NSW TrainLink intercity services," Ms Berejiklian said. "Oscars will then be moved onto the suburban network to replace S-Set trains."