"You will not see the RTA the same after this process," Mr Gay told reporters in Sydney.
"You will not see roads the same, you will not see transport the same.
"This is a major integration of what we're doing."
The new integrated transport authority will co-ordinate the state's transport services with the aim of ensuring projects are built on time and on budget, Ms Berejiklian told reporters.
"We've long been arguing that unless you establish have a truly integrated transport authority that does planning and policy across all modes of transport and roads, you won't be able to deliver those critical value customer services we desperately need in Sydney and across NSW," she said.
She said the authority will have six new divisions - Customer Experience, Planning and Programs, Transport Services, Transport Projects, Freight and Regional Development and Policy and Regulation.
It will be overseen by Ms Berejiklian and Mr Gay.
Neither Mr Gay nor Ms Berejiklian would say if there would be job losses at transport agencies such as the RTA.
Ms Berejiklian said there would be fewer "back room" jobs and more "front line" positions.
She said more detail would be released over the next 12 weeks.