About 1,000 London Tube passengers were trapped for nearly two hours when three trains were held up in a tunnel.
The Central Line was suspended
The Central Line closed after signal failures stopped the trains between Marble Arch and Lancaster Gate just before 1000 BST on Thursday.
Trains were evacuated and three people were treated for the effects of heat. London Underground is investigating.
There were also problems on the roads when Tower Bridge became stuck when it was raised as boats passed underneath.
The three Central Line trains had to be moved to Lancaster Gate, where the passengers were able to get off.
Roger Graef, one of the passengers trapped, told BBC News: "It has to make you worry about preparations for a disaster. I mean that was actually handled in an hour-and-a-half.
"I know they are working very hard. They've got a special car that gets everywhere and special uniforms but by the time they don their uniforms and got down the tracks and got to us, who knows what would have happened.
"One person fainted on our train as far as we know. Someone else was ill on a train ahead of us."
Mike Brown, from London Underground, said it was unusual that it took so long to get the passengers off the train.
He said the nature of damage to the points meant they had to move the trains backwards rather than forwards.
"Our priority is always to get people out safely, sometimes that takes a little longer than I would like it to. Safety is always the number one issue we face," he told BBC London.
Tower Bridge - an historic landmark and major Thames crossing, is thought to have been affected by computer problems when it was raised at 1340 BST.
It became stuck and traffic had to be diverted. The problem was eventually solved at 2345 BST and the bascules were lowered allowing traffic to cross the bridge.