London Underground has apologised after two days of disruption on the network saw thousands of passengers walking down tracks to safety.
On Monday, a power failure on the Jubilee Line meant rush-hour passengers had to walk along tunnels to escape.
Then on Tuesday 400 were led to safety on the Victoria line because of a defective train.
London Underground managing director Mike Brown apologised for the "distressing" experience.
He said: "I know that having to walk along the track through a tunnel is distressing.
"It is not something our customers should have to expect, and is something we always seek to avoid.
"Nevertheless, on the rare occasions when a train is stuck in a tunnel, the safest and best option is to take customers off the train."
He added: "Our customers deserve much better than the service they have had in recent days and all our energies are focused on delivering a fast, reliable and safe service."
Mr Brown denied claims by the Rail Maritime and Transport union that an overtime ban had caused most of the problems.
The RMT and the Transport Salaried Staffs Association claim Transport for London is planning to cut 2,000 jobs.
It has already held two strikes with fresh walkouts due next month.