NHS staff in Wales are being offered free travel on Transport for Wales rail services with immediate effect, the company has announced.
NHS workers will just need to show their work ID to access services to get themselves back and forth to work until 30 April.
Public transport is to operate on a reduced scale throughout Wales because of the coronavirus pandemic.
However the reduced service has led to crowding on some trains.
New timetables are now in place for trains and buses until further notice.
Announcing the move for NHS workers, Transport for Wales (TfW) said: "At Transport for Wales our primary focus is keeping our colleagues and customers safe, and to keep key workers moving.
"From Monday 23 March, Transport for Wales will provide all NHS workers free travel to and from work until 30th April on production of their NHS ID."
A statement on its website added: "We are doing all we can to keep vital services running, so that emergency service staff who are using our trains and key workers are to travel in safety with confidence."
Some passengers were reporting difficulties in maintaining social distancing on trains on Monday morning.
Hospital worker Emma Lamorte highlighted the situation on Twitter and called for more trains.
Tube travellers in London have also experienced crowded carriages, with unions saying it left transport staff feeling "furious" as they were unable to maintain social distancing.
However, other travellers in Wales reported quieter than usual carriages.
Commuter Aurora Heathfield from Bridgend, said there was an "eerie feel" on the train to Cardiff on Monday morning with carriages much quieter than usual.
"It would usually be pretty busy and you'd be looking for a seat. There was three people in my carriage," she said.
Jake Newberry from Cross Keys, Caerphilly county, said there was "hardly anyone" on his train on the Ebbw Vale line and he had expected to see more people due to the reduced timetable.
Alex Varney said the train from Barry to Cardiff was also quiet with the conductor providing advice over a speaker rather than walking through the train to check tickets.
"It was nice and quiet and nice to have some space," he said.
"Everyone was calm and pleasant and just going through their day."
A TfW spokesman said on Monday afternoon: "Whilst some services were busy this morning, on average most were 50-60% full. However, we will continue to prioritise peak periods services in order to ensure we do not create overly busy services.
""We will be monitoring the situation on a daily basis and increase capacity where necessary but we do strongly urge customers to carefully consider whether they do have to travel so that priority can be given to key workers."
Why are services being reduced?
The changes reflect the fall in demand, reduced availability of staff and the latest public health guidance, transport companies said.
Transport Minister Ken Skates said it remained "crucial" to keep some services going for key workers and supply chains.
"This action aims to balance the current significantly reduced levels of passenger demand as people follow the guidelines to socially isolate with the need to reduce the number of people required to run the network," he said.
"This contingency measure will help to ensure there are enough staff to keep services running over the coming weeks and months."
The move comes after Prime Minister Boris Johnson said people should avoid "non-essential" travel.
Operators said the closure of schools, as well as people increasingly working from home, was expected to see a further significant decline in demand.
How have bus services changed?
First Cymru, which operates services across south and west Wales, warned customers face disruption to services because "increasing numbers of staff" were self-isolating.
It said there would be a reduced timetable for services in Ammanford, Bridgend, Carmarthen, Haverfordwest, Llanelli, Maesteg, Port Talbot and Swansea.
The company also urged passengers not use cash payments to buy tickets wherever possible, to "stop the spread" of coronavirus.
Stagecoach, which operates throughout south-east Wales, said a reduced timetable would operate until further notice but had been created to ensure "critical routes are maintained wherever possible".
Nigel Winter, managing director, said the company was working to maintain essential services, safeguard jobs and ensure the long-term sustainability of the industry in a "challenging" situation.
"We also know that our bus services play a vital role in keeping the country running and ensuring key sector personnel get to work," he added.
"Our objective has been to focus resources on where we know they are needed most at this time."
In north Wales, Arriva Bus is running an emergency service but will still operate key routes "to ensure customers can continue to access critical services".
Cardiff Bus is now following a Saturday timetable for most of its services across the capital with the exception of some services which are running normally. School buses will continue for eligible children.
All Newport Bus services are also now following a Saturday timetable in "these unprecedented times", the company said.
It added: "We will maintain bus services for our customers for as long as we are able to."
How are trains affected?
Train operators across Britain will gradually reduce services following talks with the UK and Welsh governments.
However operators will still run core services to ensure key workers can get to their jobs and the flow of goods continues.
TfW said Sunday service times will be applied throughout the week though some additional services will operate to support busier commuter routes.
"This timetable has been designed to be as resilient as possible, whilst ensuring we balance a reduction in demand, availability of our people and the need to support key workers such as health, food retailers and delivery teams," it said.
The operator said advanced tickets were now eligible for refunds.