Transport Minister Chris Steel made the announcement during an address to the Bus Industry Confederation's national conference on Monday.

Mr Steel also used the speech to announce a new expert panel to oversee a plan to transition to a zero-emissions bus fleet by 2040, which will include high-profile ex-ACT politician Simon Corbell.

Mr Steel said the government had purchased 40 new Scania Euro V1 model vehicles, which would be added to Transport Canberra's fleet in late November.

The government has paid about $21 million for the new buses, which are more environmentally friendly than the older model Renault vehicles they will replace.

"The new buses will play a crucial role in modernising the existing bus fleet which has 74 buses over 25 years of age," Mr Steel said in the speech.

"As well as lowering harmful emissions and being more reliable, the new buses will be air-conditioned and importantly meet disability access requirements."

The government last week launched its second electric bus trial, as it takes another step towards phasing out diesel-powered vehicles from its fleet.

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The first trial was plagued by reliability issues, with the battery-powered buses missing 35 per cent of scheduled services.

Despite those results, the government remains committed to replacing its entire fleet of 450 diesel-fueled buses with zero-emissions vehicles by 2040.

It plans to purchase its first batch of electric buses in the next four years.

In his speech on Monday, Mr Steel acknowledged that sections of the community would prefer if the government stopped buying diesel buses immediately.

But he said that "just isn't possible", given the "challenges and scale of the transition". Major infrastructure work would be needed to support a wholly zero-emissions fleet, including "significant" upgrades to the territory's electricity grid.

Existing bus depots would have to be refurbished, while new ones would have to be built, Mr Steel said.

The ACT's workforce of diesel mechanics would have to be re-trained so they had to skills to work on electric vehicles, he said.

Mr Steel said the government was developing a strategy to guide the 20-year transition, which would be overseen by a new expert committee.

Mr Corbell, a former ACT deputy chief minister who now works as a renewable energy consultant, has been handpicked to sit on the committee alongside Australian Manufacturers Workers' Union official John Stewart and university academics Dr Lachlan Blackhall and professor Peter Newman.

Professor Newman, who works at Curtin University, is a well-known advocate for trackless trams as an alternative to light rail.

Mr Steel and Major Projects Canberra Duncan Edgehill last week dismissed the emerging technology as "pretty novel", as they raised doubts about its cost and safety.

In a statement on Monday, Mr Steel said the four members of the committee had been selected because of their "expertise and ability".

The committee was expected to meet before the end of the year, with the transition plan expected to be finalised by mid-2020.