Rodd Staples, who was sacked as transport secretary last November, tells a NSW parliamentary inquiry he had serious concerns about rail safety compromises resulting from a state-owned corporation's focus on turning a profit.

Rodd Staples, who was sacked from his role as transport secretary last November, on Monday gave evidence at an upper house inquiry into the state-owned Transport Asset Holding Entity (TAHE).

TAHE was established by the NSW government to manage the state's $40 billion rail assets and infrastructure in July last year.

It was also designed to help achieve budget surplus because any funding going to the corporation could be defined as investment instead of expenditure, therefore not impacting the budget's bottom line.

Mr Staples told the inquiry he was so "uncomfortable" with the way TAHE was operating, he took his concerns to then-Premier Gladys Berejiklian.

"My observation was the key driver for TAHE was to make sure they could present the budget in a fiscally different way," he said.

Around the time his contract was terminated for no reason, Mr Staples was in tense negotiations with the NSW Treasury.

He was trying to develop a workable model which ensured the safety of rail operations when the infrastructure was going to be managed by a state-owned corporation which had to generate a profit.

"Certainly I was very uncomfortable," Mr Staples said.

"There was concern within Transport including myself around TAHE's readiness to take on the role of the asset custodian." 

Mr Staples raised concerns medium-to-long term safety could suffer because of TAHE's commercial objectives.

"You'll be faced with a conflict of should I invest in the rail asset and maybe a new signalling system versus invest in a property development that would generate a higher return," he said. 

He said there were also accountability issues between Sydney Trains and TAHE. 

"The issues around who was really going to control maintenance would be a very good example of the ambiguity and uncertainty," he said.

He told the inquiry he'd also received advice from consultants there was a $10 billion hole in the financial benefit projections which resulted in a stoush between the transport department and Treasury.

The inquiry heard he was ordered by the Treasury secretary Michael Pratt to "find a way to make it work".

Mr Staples said he initiated a meeting with Ms Berejiklian after TAHE had been established.

"I went in and said we were getting on with the implementation of TAHE," he told the inquiry.

"But that I was wrestling with my capacity to lead with the constraints that TAHE was imposing."

He said at the time he was still committed to remaining as transport secretary in the short term but was later sacked.