Signal failure hits rail services between London and Essex
Passengers are experiencing delays of up to 40 minutes on train services between Liverpool Street and Harwich in Essex because of signal failure.
Some air services from Stansted are also hit and passengers are advised to check with airlines before setting out.
Traffic is running normally on the M11 but Paul Henry, from the East of England Ambulance Service, said some roads are still dangerous.
About 45 schools are closed and 10 others are expected to open later.
The cold conditions have continued into Monday with police warning drivers to take extra care after up to eight inches (18cm) of snow fell.
Essex Police are urging people only to drive if necessary as many roads are icy after temperatures fell during the night.
There is also the chance of some sleet or rain on Monday and Tuesday, the Met Office said.