Citing official NSW Treasury figures, Opposition spokesman for Transport Ryan Park said the cost of private consultants had increased from $10,860,000 in 2013-14 to $23,188,000 in 2015-16.

He said the money spent on contractors, budgeted at $114 million for 2014-15, blew out to $159 million.

The figures also showed that $552,000 was spent on overtime costs for transport workers in 2011-12. In 2014-15 the figure had grown to $100,968,000.

"This government needs to urgently address the amount of money it is spending on external consultants and examine why this work can't be carried out by either existing staff in the Transport portfolio or the hiring of new staff if necessary," Mr Park said.

"This is a huge increase in the amount of taxpayers money that is being used to pay for consultants and contractors whilst at the same time the government is looking at continuing to cut frontline staff at stations and security guards, both of which are designed to keep people safe and make using public transport easier".

In budget estimates on Tuesday, Labor MP Penny Sharpe also grilled the Minister for Transport and Infrastructure Andrew Constance over what she said was a $500,000 contract taken out by Transport for NSW for the provision of actors.

"Have you been paying actors to help train staff within Transport for NSW," Ms Sharpe asked.

Mr Constance said he would not apologise for spending money on advertising campaigns to raise awareness of new projects, but would not answer whether the department was paying actors.

Ms Sharpe said the website from the acting company said they had been contracted to playing "vandals on a train trying to avoid detection".

Transport for NSW secretary Tim Reardon later told the hearing that the contract was for staff training, and was standard among government departments.

A spokesman for Mr Constance said there had been no cost increases for overtime and the change in numbers was a result of a restructure of Transport for NSW which meant a larger number of employees were included under the same category. Consultant and contract costs had increased in line with the government's major infrastructure building agenda.

Mr Constance said Labor spent more than $22 million on consultants in their last year in office.

"We make no apologies for cracking on with major transport projects that are going to transform this city and this state," he said.

"Unlike Labor, we don't waste hundreds of millions of dollars on projects and then cancel them. We build what we promise."