A Fairfax analysis of new transport statistics provides deeper insight into rising overcrowding on the city's ageing rail network, which has led passenger numbers on some lines to increase by more than 10 percentage points.

The analysis identifies the stations and commuters bearing the brunt of Sydney's 10,000 new peak-hour passengers each year.

Commuters getting on a 3.25pm service from Redfern to Helensburgh, a suburb on the city's southern outskirts, halfway to Wollongong, have to endure a train with more passengers than seats the longest of all: 50 minutes.

The Herald went along for the ride on Friday and found stairwells lined on what passengers said was a comparatively quiet school-holiday Friday.

Chris McIntosh from Kangaroo Point said open spaces were so rare that commuters had to be prepared to fight to displace baggage.

"I just say, 'Have you bought two tickets?'," Mr McIntosh said. "That's my line".

Another 3.25 regular, young car mechanic Josh Richards, said he could not recall getting a seat after a shift on that leg of his two-hour journey home to the Illawarra.

The Helensburgh train is unusual because Sydney's morning trains tend to be the most crowded, because passengers arrive in more concentrated patterns.

A new interactive on smh.com.au allows readers to calculate a long-proposed but little enacted remedy: staggering their morning commutes, to leave earlier or later and catch a less-crowded train.

Commuters at Ashfield, for example, should try to avoid the 8:13 am to the city. With 180 passengers per 100 seats, this is the worst time and place on the network to get a seat, according to the data.

The advent of the Opal card has already led to the introduction of an off-peak fare designed to change commuter behaviour.

The state's pricing regulator wants to see those discounts raised.

In Melbourne, all train travel before 7.15am on a weekday is free.

"Whatever happens [overcrowding is] going to definitively get worse for a few years," says Sydney University lecturer in Transport Management, Geoffrey Clifton.

Strong population growth, especially in Sydney's centre, is expected to only add to the choke points at the major junctures in the transport network.

The analysis is based on a Transport for NSW survey of peak period trains at Sydney's busiest stations. Many are key junction points on the transport network, such as an interchange at Lidcombe or Milsons Point, the last stop on the North Shore line.

But Sydney's second-most crowded station, Harris Park, is surrounded by a population that has grown one-third in the past five years and which is a major centre for migrants. One in two peak period trains leave Harris Park with standing room only.

A spokeswoman for Transport for NSW said that demand on Sydney's train network was growing at similar levels to other major international cities but the new Sydney Metro project would increase its carrying capacity by more than half to 40,000 passengers per hour.

The first stage, an $8.3 billion metro line from northwest Sydney to Chatswood is due to open in 2019. Further development, including a new metro line between Chatswood and Bankstown, will open in 2024 but the final cost of that project is not clear. The government says that satisfaction with train services has grown over the past three years and stands at 90 per cent.

A train which is 100 per cent full, has as many seats as passengers but 130 per cent full is the benchmark the transport department uses for overcrowding, the point at which passenger numbers risk the train running late.