The NSW government insists it will have enough bus drivers for a new train replacement service as the year-long closure of a busy Sydney rail line looms.

More than 50,000 trips a day are made on the T3 line, which is due to shut between Sydenham and Bankstown by the end of October so the railway can be converted for driverless Metro trains.

So far, 140 of the 200 drivers needed to operate the pink Southwest Link buses have been hired.

As recruitment for the remaining 60 drivers ramps up, Transport Minister Jo Haylen has pitched the crucial jobs to "parents who are looking for extra cash", with part-time and flexible shifts available.

"We have seen recently retired or semi-retired people coming on board, as well as people with family and caring responsibilities," Ms Haylen said.

Former disability support worker Allison Smith is one of the new recruits.

"I'm really enjoying my customers getting on and off the bus," Ms Smith said.

"The customers love the female drivers."

Full-time drivers along the temporary route will be paid a salary of $70,000 a year or about $35 an hour.

'Totally unachievable'

Transit Systems NSW and U-Go Mobility have been contracted to run Southwest Link. Both companies have offered $6,000 bonuses for drivers to join.

But the Transport Workers Union (TWU) doubts enough drivers will be hired and trained in time for the railway closure.

TWU NSW Branch Secretary Richard Olsen said the pay would not be enough to convince people to take up a career in bus driving.

"You would do a lot of other work and occupations that paid that much, plus more, before having to put up with the issues bus drivers put up with each and every day," Mr Olsen said.

He said it was unrealistic to think enough new drivers would be ready in time because of the amount of training required.

"It would seem to me to be totally unachievable to achieve a further 60 more drivers in such a short period of time."

Anyone with an unrestricted car licence is encouraged to apply, with training offered on the job.

"Someone with a car licence can take up to six to eight weeks to be fully competent and trained," Transit Systems NSW Managing Director Daniela Fontana said.

The government previously said the T3 Bankstown line would close between July and October.

Transport for NSW Coordinator-General Howard Collins said the latest projection has the line shutting in September or October.

The agency has contingency plans in case not enough drivers are ready on time, but Mr Collins said it would not be to the detriment of other services.

"We're not going to impact existing background buses by removing drivers from their routes onto this," he said.

Even with Southwest Link running at full capacity, commuters are being warned to prepare for delays. The express and limited stops services will still take longer than the train.

"It will add several minutes, if not tens of minutes of time to your journey," Mr Collins said.

Ms Haylen admitted people who use the T3 line were facing an inconvenient 12 months.

"We know it's going to be painful, but in the end the result will be worth it," she said.