Trains operators across Britain will gradually reduce services from Monday, amid falling demand because of the coronavirus pandemic.
The government said it had agreed the plan with the rail industry to reflect the fall in passenger numbers, while keeping vital services running.
Operators will still run core services to ensure key workers can get to their jobs and the flow of goods continues.
It comes after the PM said people should avoid “non-essential” travel.
Train operators across the country had already begun cancelling services because of staff being off sick or self-isolating and a collapse in demand.
And Transport for London has announced up to 40 Underground stations will be shut until further notice, while bus services will be reduced.
Buses in the West Midlands and Greater Manchester are also among those to be cutting services.
The reductions to services will be keep under review, with operators communicating any changes with passengers, the Department for Transport said.
To minimise disruption, services will be reduced progressively, but over the longer term, the department said there would be “a gradual move towards introducing reduced services on wide parts of the network”.
The plan will also ensure people can travel to medical appointments and key freight services can continue to ship vital goods where they are needed, it added.
Transport Secretary Grant Shapps said: “We are taking decisive action to protect the public which means reducing travel for the time being, whilst still ensuring key worker heroes can get to their jobs to keep this nation running.
“We continue to work closely with the industry to develop measures that protect operators in these challenging times.”
Mr Shapps told MPs on Tuesday that rail companies, bus firms and airlines could be temporarily nationalised to help them through the outbreak.
Robert Nisbet, of the Rail Delivery Group, which represents train operators and Network Rail, said the measures would allow trains to continue to operate over a prolonged period with fewer railway workers, whose safety “remains front of mind”.
Passengers are advised to check the time of their train on the National Rail Enquiries website before travelling, he added.
Similar measures have been agreed by the Scottish and Welsh governments
The Scottish Transport Secretary said operators would be moving to a “reduced timetable”, while the Welsh Government Minister for Economy and Transport said services would also be reduced in Wales from Monday.