The timetable, released on Tuesday and due to come into force on October 20, has drawn substantial criticism from South Coast commuters.

Those at smaller stations in the Illawarra's north will be most disadvantaged, with many having to catch earlier trains to get to work on time, with fewer trains stopping for them.

In the evening period of 5pm to 6.30pm, the number of trains leaving Central to Wollongong is halved from eight to four.

The Transport for NSW spokesman said not all the eight services between 5pm and 6.30pm currently provided were useful for South Coast commuters.

"Under the current timetable there are eight trains to Wollongong between 5 and 6.30pm - however they are not all providing a viable service for South Coast customers," he said.

"Three are slow suburban services which cater for customers in the Sutherland Shire and dwell for around 10 minutes at Waterfall before extending to the South Coast and providing an all-stops local service.

"Three are fast services that carry most people from Central to the South Coast and two become all-stations services between Thirroul and Wollongong.

Winners and losers from new timetable

"The new timetable increases the number of fast services from three to four and provides connecting services to customers travelling to local stations. This is a better outcome for most customers, with more faster, viable services," the spokesman said.

He said the changes improved services at the most popular time during the rush home - which was before 5pm.

"The most popular afternoon peak South Coast Line service currently departs Central at 4.41pm, after a service gap of 45 minutes to Wollongong.

"The new timetable will provide a new South Coast departure at 4.24pm to provide more choice for customers during the most popular travel period."

He said the new timetable also provided a fast South Coast service every 20 minutes or so between 3.54pm and 6.06pm.

Read new timetable for South Coast Line

When asked if the four trains that will leave Central between 5pm and 6.30pm would have the same number of carriages as the eight in the current timetable, the spokesman focused only on what he called the "key services".

"Of the five key services departing Central between 5pm and 6.30pm in the current timetable - three have eight carriages and two have four carriages," he said.

"The new timetable will have four services departing Central between 5pm and 6.30pm, all with eight carriages, so there is no decrease in capacity."

Another change is that the peak trains start and finish at Bondi Junction rather than Central to ease the trip for those commuting to the eastern suburbs.

"Increasing the number of trains starting at Bondi Junction will mean fewer Illawarra and South Coast customers coming from the city and eastern suburbs will have to change trains, reducing their overall journey time and making services more convenient," he said.