Rail services in parts of eastern and southern England will be cancelled in anticipation of heavy snow.
Greater Anglia, which serves Norfolk, Suffolk and Essex, is ending services early on Monday at 10pm to enable trains to return to depots and stations before the forecast snow storms begin.
Some empty trains will run throughout the night in a bid to keep lines clear for the morning commute.
A limited timetable will be in place on Tuesday and Wednesday between 6am and 10pm.
The plan means more than 200 Greater Anglia trains have been cancelled.
Network Rail, which manages Britain's railway infrastructure, is focusing its efforts on keeping the main routes open - Norwich to London, Southend to London, Norwich to Cambridge and Cambridge/Stansted to London.
There will be no trains or rail replacement buses on the rural routes of Norwich to Lowestoft, Great Yarmouth and Sheringham, and Ipswich to Felixstowe and Lowestoft.
Other routes will run with a reduced service.
Passengers were also warned to expected delays and cancellations on c2c, London Overground, South Western Railway, Southeastern, Stansted Express and TfL Rail.
If the weather is not as extreme as forecast, Greater Anglia and Network Rail have pledged to "work hard" to reinstate services as quickly as possible.
Greater Anglia's train service delivery director Richard Dean said: "We apologise for the inconvenience that this reduced service causes customers.
"The last time such heavy snow fell in this region was over 25 years ago.
"In extreme conditions such as these, we work hard with Network Rail to keep key routes open, using snow ploughs, points heaters and mobilising all staff to clear snow off platforms and heat up and de-ice trains.
"Volume of traffic on some routes keeps snow from settling too deep, like on roads, but not on rural routes.
"We are committed to keeping our customers safe in all conditions and the last thing anyone wants is for customers to be stranded on a cold train in the middle of a blizzard in rural Suffolk or Norfolk."
Network Rail said it will attach heaters and NASA-grade insulation to points - the section of rail that moves to enable trains to switch between tracks - to prevent ice forming.
Anthony Smith, chief executive of watchdog Transport Focus, said: "We know there can be frustration when trains are cancelled and timetables altered for snow that doesn't appear or is lighter than predicted.
"The industry needs to better communicate why the decisions are made when they are."