Why Do Tube Trains Stop When You Lean On The Doors?

Why Do Tube Trains Stop When You Lean On The Doors?
Lean at your peril. Image: Shutterstock

We would hazard there's not a single person reading this who hasn't had their rush-hour standing snooze interrupted by an irate tube driver imploring passengers not to lean on the doors.

Looking at the faces of those nearby as the train struggles to get going, it's clear some think the driver is overreacting a tad as he or she berates a wedged-in punter for what seems a trivial offence.

So what catastrophe befalls such a train bulging with commuters? We duly extracted the required knowledge from the 'rolling stock professional head' (which we like to picture as a giant brain buried deep beneath Paddington station).

The 'sensitive edge'

Move your ass, or your ass is going nowhere. Image: Shutterstock

All tube train doors have a safety circuit, known colloquially as an interlock but more fancily as a 'sensitive edge'. If the doors are open to any degree, the circuit is broken and the power to the train's propulsion system is cut. Ostensibly this is to prevent someone being dragged along half in and half out of a train, and all the mayhem that would evoke.

However, the design of the train doors is such that someone leaning heavily on the door is applying a pressure to the connecting points, which the train's system interprets as a gap in the interface between the door and the frame. In short, the doors don't know if the circuit is broken by someone or something trapped between them, or someone leaning on the inside.

Are some lines more susceptible than others?

Why would you want to upset him WHY?

The brain says no. It used to be more noticeable on the older D and C Stock of the District, Hammersmith & City and Circle lines, as those were able to move off a short way and then come to a halt if the door sensed an obstruction.

On newer stock, such as the 2009 Stock on the Victoria line and S7 and S8 Stock on the Circle, District, Hammersmith & City and Metropolitan lines, the door circuitry operates on the same principle but the train won't even begin to move off if it detects a break in its sensitive edge. On the newer stock, the doors will attempt to reopen (up to 45mm) up to three times to allow an obstruction to be removed. If it's still there, the driver may well then manually open the doors fully... and at this stage, likely get a bit exasperated with everyone.

If someone starts leaning on the door once it's already departed from the platform, it's not safe for the driver to open the doors, so we just all have to wait until Mr or Mrs Lean stop doing what they're doing.

So there you have it: the next time you hear a driver demanding you shift your backside from its comfy berth wedged between the tube doors and four other cheeks, they really do mean your ass is going nowhere if you don't shift it.

Last Updated 24 February 2020

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