this is off topic kind of, im not very good at staying on topic but i
think theres some kind of clever thing to stop piccadilly line trains
near Earl's Court eastbound/northbound from going into the district
line tunnels which are smaller, something to do with cylinders of
mercury hanging in mid-air somehow, the idea is if the piccadilly line
train goes onto the wrong track the train will be big enough to smash
the cylinders and the mercury short circuits the track so the train
won't go any further, its really clever

so if they can do something like that wouldn't it be no more difficult
to set something up that short circuits if the train goes the wrong
way down the track?