According to Transport for NSW’s latest customer satisfaction index, conducted in May and released on Thursday, 90 per cent of respondents were at least partially satisfied with the overall service, a 1 per cent increase on the previous survey in November 2013.

The issue that caused the most dissatisfaction was the frequency of trains, which irritated 29 per cent of those surveyed.

This was a 2 per cent increase since November 2013, and a 5 per cent increase from the last survey before the train timetable was revised.

There was also a wide gap to the  next biggest complaint – availability of parking near stations, which 16 per cent cited as a problem.

The surveys are  undertaken by Transport for NSW twice a year. Commuters are interviewed in person while riding a train.

The May 2014 Customer Satisfaction Index features responses from more than 34,000 public transport users across the state.

They were given a range of statements and asked whether they agreed or disagreed with them.

Overall, the South Coast scored the second highest level of satisfaction - at 90 per cent. Only commuters in the Hunter were happier.

The South Coast line also recorded the second lowest level of dissatisfaction overall, at 5 per cent. The Hunter was again in top spot, with 3 per cent.

The most troublesome line is Carlingford in north-west Sydney, with a dissatisfaction rating of 21 per cent.

Transport Minister Gladys Berejiklian said the results of the survey showed the government was on the right track.

‘‘We know we have plenty of work to do, but overall people using public transport are telling us they are seeing improvements,’’ Mrs Berejiklian said.

‘‘We will use this feedback to ensure we see even better results again next year.’’