The description for tonight's episode says "For Tube drivers, their worst fear is somebody jumping or falling in front of their train. We follow what happens when this fear becomes a distressing reality for two drivers.
Also, we meet the crews of the Tube's specialised emergency response units as they scramble to deal with any eventuality on the Underground, from accidents and injuries to mysterious obstructions on the line."
A couple of years ago Channel 4 screened a 30 minute documentary called One Under. It looked at Tube drivers who gave first-hand accounts of their experiences with the suicides. The interviews were moving and give an insight into the initial shock, anger, attempts at understanding, appearance at Coroner's Court, right through to the permanent marks the suicide left on their lives.
You also might remember the comedy Three and Out starring Mackenzie Crook. He played a Tube driver who learns about the "Three and Out rule". The rule says that if a Tube Driver experiences three people who are hit & killed by their train (a "one under") within a month they get laid off work and receive 10 times their annual salary as a pay off. This was obviously a spoof and not a real rule at all but led to quite a kerfuffle with the train drivers union Aslef & the London Underground when it was screened.