With cold temperatures causing chaos in the last few days, people have started noticing a strange blue light on London Underground trains but only a few know what it actually means.
One Londoner recently spotted the light and was left baffled, taking to Reddit to ask for information.
They penned: “Saw this on train 032 arriving at Hammersmith heading eastbound. Only on this middle carriage. Usually this light turns white when a train is ready to depart under ATO but I’ve never seen it lit up blue, and I believe this is still a manually driven section – anybody got any idea what it means?”
Others were quick to explain in the comments section with one person saying:”De-icing unit in operation. The train sprays some deicing fluid on the power rails.”
And they were completely right. According to Transport for London (TfL), a blue light sometimes illuminates on the front carriages of some Circle, District, Hammersmith and City and Metropolitan trains.
If the light turns blue, then the train is equipped with, and may be deploying, a de-icing solution.
Many people are also accustomed to seeing a white light. This is because on the Tube lines equipped with automatic train operation (ATO), there are lights located on either or both the trains or platforms which indicate whether the train is about to depart, MyLondon reported.
On the lines which use ‘S Stock’ or ‘2009 stock’ Tube trains – the Circle, District, Hammersmith and City, Metropolitan and Victoria lines – when trains are about to depart (usually within 15 seconds), a white light will illuminate above the windows on the carriage exterior.
If you see a white light and you’re hoping to hop on one of these trains, it is not recommended to take the risk as departure is imminent and getting trapped in the doors can lead to serious injury.
On the Central, Jubilee and Northern lines, these lights are located at the end of the platforms, nearest to the front of the train in the direction of travel. When the light on the platform changes from red to white or lights up white, it’s a signal that the train is ready to depart.
In both cases, the light remains a steady white and shouldn’t be mistaken for other flashing white lights elsewhere on the train or platform as they could signify different things.
The Bakerloo, Piccadilly and Waterloo and City lines, along with some sections of other lines that don’t use automatic train operation, and still utilise traditional ‘traffic light’-style signals.
Therefore, passengers need to rely more on listening to announcements and the familiar door closing chime to know when it’s time to get moving again.