Hundreds of trains have been cancelled on the region's network as snow and sub-zero temperatures are forecast. But why do trains stop running in cold weather? Here is everything you need to know.

What effect does snow have on rail services?

According to the Network Rail website, when trains slow down to approach a station or set of points this can cause snow to compact on the rails and turn into solid ice.

This clogs up the points and stops them from working and can also coat the electrified rail, disconnecting trains from the power they need to run.

Do other forms of weather affect trains?

According to the company's website ice sheets can dislodge and damage passing trains and the steel rails can freeze together if they become too cold. If this happens signals stay red and trains can't move.

Wind is another problem as if it causes snow drifts deeper than 30cm trains can't run safely unless they're fitted with ploughs.

How does Network Rail prepare for wintry weather?

Specialist forecasters keep Network Rail informed of any severe weather risks, and it runs a colour-coded system to alert controllers to the response they need to take.

Network Rail also works with train companies, such as Greater Anglia, to develop special winter timetables and also run empty trains overnight to help keep the tracks clear of snow.

How does Network Rail respond to extreme weather?

When conditions are very serious Network Rail introduces temporary speed restrictions for trains. The website states it may also take preventative measures, sending out ice patrols to remove ice from overhead lines.

Sometimes lines will be closed if there's been a landslip or while heavy snow is cleared away.