By ITV Wales reporter, Mike Griffiths.
The South Wales Metro is one of the most ambitious infrastructure projects carried out in Wales in decades.
It'll mean brand new trains, and more regular services on the network, with a particular emphasis on the 'Core Valley Lines' running to Cardiff.
New electric 'tram trains' will run on the lines from Treherbert, Merthyr Tydfil and Aberdare to Cardiff - allowing four trains to run per hour on each line on weekdays.
The Coryton and Rhymney lines will also be electrified and run new vehicles.
Before the trains can run, a huge amount of preparatory work has had to happen.
Tracks have had to be replaced, and in some cases doubled, to allow for the greater frequency of services.
Large pylons also have to be erected to carry the overhead electric cables.
ITV Wales has had exclusive access to watch the electrification work taking place.
Transport for Wales' Senior Construction and Safety Assurance Manager Jamie Meredith explains how the work has been carried out:
"Much of the work takes place at night, when our trains are not running, because that's the safest time for our engineers and our track staff to get out.
"It happens most nights, most evenings, and most weekends, and sometimes there are temporary periods of disruption where we have to stop trains.
"There have been extensive track upgrades, line speed improvement upgrades.
"We've had to install passing loops, and then the electrification system, in order to improve the frequency of our services, in order to run the new fleet of trains which will be greener, faster, more capacity and hopefully much more reliable."
Leyton Powell, TfW Director of Safety and Sustainability said: “Installation of the first electrical lines is a major step forward for us at TfW and once completed, this programme of works will provide greener transport for the future.
“However, it’s fundamental that we highlight that electrification work is now underway and therefore the public must understand the risks and dangers. As always, trespassing on the railway is dangerous and it’s important that people obey the rules as they are for their own safety.”
The pandemic and rising costs have had an impact on the project, with the Welsh Government admitting the launch has slipped to 2024.
A spokesperson told ITV Wales "Despite earlier delays, progress is now being made at pace, with the introduction of the new Stadler 231 trains in January and the majority of work on the rail line scheduled for completion in 2024.”
When Transport for Wales took over the Wales & Borders franchise in 2018, it's fair to say expectations were high.
Aside from the running of services, the development of the South Wales Metro project - a vastly improved rail and bus network - was also a key component.
But the pandemic has had a significant impact. Dramatic falls in passenger numbers meant the Welsh Government had to step in as 'operator of last resort' in 2021 - effectively nationalising the company.
Inflation and the costs of materials mean the project is also likely to cost far more than initially projected.
Transport of Wales points to improvements that have already been carried out, such as station improvements, the replacement of the ageing Pacer trains, and newly-refurbished stock being introduced across the network.
But the launch of the Metro project - with its promise of a 'turn up and go' train service for the areas it covers - is eagerly awaited.
Plans for a Swansea Bay and North Wales Metro are also at early stages - but will require consent and funding from the UK Government.
With the Welsh Government encouraging a move away from car use, offering convenient alternatives is vital.