London Underground's managing director Mike Brown apologised to Tube passengers after two days of disruption which saw thousands of travellers led along tracks through underground tunnels after trains failed.
Mike Brown said many people had endured difficult and in some cases "severely interrupted" journeys to work.
Around 400 passengers on London Underground's Victoria line were stuck in a tunnel near Seven Sisters after a defective train caused huge delays in yesterday's rush hour.
There were also delays on other parts of the system, including the Northern and Circle lines, because of signal failures and track problems.
The Tube delays followed Monday's power failure on the Jubilee line which led to thousands of passengers being stranded in tunnels before being led to safety along the tracks.
Mr Brown 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, as soon as it becomes clear that we will not be able to arrange for it to be moved within a reasonable timescale, the safest and best option is to take customers off of the train.
"We are now looking closely into the circumstances of both incidents to ensure we get to the root causes and take the necessary steps to prevent further occurrences.
"Unfortunately several unrelated problems have affected some other lines in the past two days, compounding the disruption for passengers. Again, we are examining the detailed causes of these to avoid re-occurrence."
Mr Brown denied claims by the Rail Maritime and Transport union that an overtime ban had caused most of the problems, except on the Metropolitan line where a programme of essential maintenance on some trains was being delayed by the dispute over job losses.
"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."
The RMT, and the Transport Salaried Staffs Association (TSSA), has already held two strikes and is threatening fresh walkouts next month, claiming Transport for London is planning to cut almost 2,000 jobs.