Transport plans for London's Olympics face their sternest test ahead of what is expected to be the Olympic Park's busiest day since the Games opened.
奥运会开幕后，奥林匹克公园最繁忙的一天将到来，伦敦奥委会的交通方案面临最严峻的考验。
Transport problems are said to have caused long queues for the high speed Javelin train service
More than 200,000 people will be at the park later, including up to 80,000 who will descend on the Olympic Stadium for the start of athletics events.
The Central Line, which serves the Olympic Park in Stratford, is currently experiencing severe delays.
British hopes for medals are in rowing, track cycling and swimming later.
Problems on the Central Line followed a signal failure at Bethnal Green station, London Underground said. Tickets are being accepted on National Rail services in the area, while Transport for London are encouraging those attending the Games to use alternative lines and stations close to the Olympic Park.
The BBC's Claire Heald, at the Olympic Park, said the Stratford area was congested（堵塞的） .
Team GB have risen to fifth in the overall medal table with five golds after three were secured on Thursday.
Among the gold medallists on day six were track cyclist Sir Chris Hoy. His victory, with Philip Hindes and Jason Kenny in the team sprint, represented his fifth Olympic title and equalled rower Sir Steve Redgrave's record British, Olympic gold medal haul.
Meanwhile, hopes are high for rowers Katherine Grainger, who has three silvers from three previous Olympics, and Anna Watkins in the double sculls, swimmer Rebecca Adlington, who defends her 800m freestyle title, and the men's track cycling pursuit team.
Highly fancied heptathlete Jessica Ennis also gets her campaign under way at the Olympic Stadium, in the 100m hurdles, the high jump, the shot put and the 200m.
Other British athletes in action on Friday will include world champion Dai Greene in the men's 400m hurdles heats and defending Olympic champion Christine Ohuruogu in the women's 400m.