[michaelt]

  Drivers are trained in passenger management, and every so 
  often they need that training to deal with fights, 
  illness, suicides, or all the other messy things that 
  happen on a public transport system

As I understand it in a lot of the London trains it's not possible to move between carriages - so the driver can only deal with fights, illness, suicides etc over CCTV or by stopping at a station?

[yangyang]

There are doors but they are not for use in normal circumstances. The new Victoria Line trains were initially supposed to be "space trains", open all the way through, but didn't actually end up getting built like that.