Stadler has commenced testing of its Fast Light Intercity and Regional Trains (FLIRTs) for Transport for Wales (TfW) in Switzerland.
The trains are being built as part of the Wales and Borders network transformation.
They will later be sent to South Wales for additional trials on the network, where they will commence services from the end of 2022.
FLIRTs will be introduced under TfW’s transformational strategies and the extra 35 trains will operate within the South Wales Metro network.
The Class 756 tri-mode FLIRTs will offer services on the Rhymney, Coryton and Vale of Glamorgan Lines while the Class 231 diesel FLIRTs will run between Cardiff and Ebbw Vale, Maesteg and Cheltenham.
Transport for Wales CEO James Price said: “These brand-new trains, with better facilities all-round, will provide a modern service for the people of Wales.
“We’ve already started testing on some of our new trains within Wales and I’m pleased our Stadler FLIRTs are now being tested in Europe and will then be sent to us for testing on our network.”
Apart from increased capacity, the new trains will run more frequently and provide enhanced amenities, such as information screens, power sockets, and air conditioning.
Each train will have the capacity to accommodate up to six bikes, and level-boarding to help commuters with limited mobility.
Stadler project manager Sandro Muster said: “With more than 1,970 of them sold in 21 countries, it is reliable, innovative and suited to a wide range of climates and geographies, including cities and regions alike.
“Of the 35 FLIRTs for Transport for Wales, 24 units will be tri-mode, capable of running on diesel, overhead electric wires, as well as battery power, underscoring Stadler’s green credentials and commitment to decarbonisation.”
Last month, TfW reactivated an improved the rail service between Holyhead and Cardiff, increasing capacity and fully renovating intercity carriages.
It also announced the procurement of additional Mark 4 carriages, which will be deployed between South Wales and Manchester from next year.
In addition, trials have started on the brand-new Class 197 trains that are being put together in Newport.
Earlier this year, nearly eight Class 769 trains were launched, and the Pacer trains were withdrawn from service this summer.