Spectators travelling to the Games today have been affected by delays on three Tube lines.
A signal failure at Acton Town in west London caused a suspension of the Piccadilly line between Hammersmith and Northfields/Uxbridge, with severe delays on the rest of the line.
A signal failure at Earl's Court, close to the venue where the Olympic volleyball is taking place, led to delays on the District line.
And there were also delays in the morning rush-hour on the Jubilee line due to a signal failure at Wembley Park.
Transport for London (TfL) warned that the Jubilee and Metropolitan lines would be particularly busy later with Olympic football taking place at Wembley Stadium.
Baker Street, King's Cross and Green Park Tube stations were also expected to be very busy.
TfL also said Earl's Court would be busy due to the volleyball, while large crowds could be expected at Greenwich for the equestrian event.
The transport has generally coped well with the hordes of spectators attending Olympic events.
The Tube carried a record 4.4 million passengers last Friday and the number of passengers using West End Underground stations last Saturday evening was 27% above the norm.