New route plans created by State Transit, the government-owned bus company, will soon allow it to run the same number of daily services as currently exist in Sydney but with 36 fewer buses and 86 fewer drivers.

But those plans have angered the Rail, Tram and Bus Union, which says the government should turn those buses and drivers into extra daily services. With 36 extra buses, more than 350 extra bus services a day could be put on in Sydney.

The changes themselves are uncontroversial and long overdue. They will allow State Transit to cut the number of buses that run "dead," or empty, by changing where they begin their routes, meaning commuters should not notice a difference.

For instance, some buses that start in Sydney's north are stored overnight in State Transit's Tempe depot, meaning drivers begin their day taking empty buses across town.

State Transit estimates its "route optimisation" program will save 38,000 kilometres a week in “dead running”.

"Overall, 36 fewer buses and 86 fewer drivers will be needed," a spokesman said. "This will occur over time by natural attrition. No bus driver will lose their job."

But those "savings" have angered the union, which says they should be tipped back into the public transport network.

"If you can save 35 buses by being more efficient in the system, those buses need to be put back into struggling, overcrowded corridors," the secretary of its bus and tram division, Chris Preston, said.

Gary Way, the division's president, said the route changes "should have happened years ago" and accused the minister of breaking a promise not to cut frontline resources.

If they were reinvested in the network, another 36 buses could be used to add as many as two new metro bus routes.

State Transit is under pressure to cut costs as it faces an open threat of privatisation. The organisation's chief executive, Peter Rowley, has already tried to renegotiate a number of conditions included in its most recent workplace agreement with staff.

Asked why the savings were not being reinvested in new services for commuters, the Transport Minister, Gladys Berejiklian, said: "I have been very clear that I expect State Transit to become more efficient and deliver improved services to customers.

"State Transit's advice to me is no driver will lose their job as a result of this initiative, and the bottom line is that as we continue to deliver more services over time, we'll be needing more frontline staff to deliver those services.”

State Transit has been talking about implementing these sort of "route optimisation" plans since at least 2007.

Previously, the bus operator planned routes separately at each depot. But routes are now planned across bus regions.