"Clive D. W. Feather" wrote in message
...
In article , Christine
writes
Presumably such tight to gauge tunnels exist on the section of line
between Kentish Town and Farringdon.

It's a double-track tunnel.

I wonder if the decision is based upon the premise that if two trains,
travelling in opposite directions, became stuck in the tunnels it would be
impossible to detrain passengers using the side doors, either to the cess or
the six foot. Hence the requirement for end doors.