Transport for London (TfL) has said it is "sorry" about the death of a female cyclist who was killed on a cycle "superhighway" in east London.
On Friday, a 34-year-old woman became the second person in three weeks to die at the busy Bow Roundabout junction.
The victim, who is yet to be named, was pronounced dead at 16:45 GMT.
The 29-year-old driver of a lorry involved in the crash was arrested on suspicion of causing death by dangerous driving.
He was released on bail to return to an east London police station on 7 December pending further inquiries.
The London Cycling Campaign (LCC) group demanded an immediate redesign of the roundabout.
It said the roundabout was dangerous because the cycle superhighway stopped in the middle of the Bow roundabout.
LCC's chief executive Ashok Sinha said: "We're appalled at this latest preventable death and are fearful of what may happen when large numbers of cyclists are expected to tackle this junction on their way to and from the Olympics next year.
"We can't understand how this junction can form part of what is one of the Mayor's flagship cycling projects: it must be redesigned now."
TfL surface transport manager Leon Daniels said: "We are extremely sorry to learn of the tragic death of a female cyclist, following a collision with an HGV on the Bow Road roundabout on Friday evening.
"Our thoughts are with her family and friends. I have visited the scene and both TfL and the police have launched inquiries which will report as quickly as possible."
Last month a 58-year-old man was killed in a collision with a tipper truck.
Four priority lanes for cyclists, branded cycle superhighways, have been painted blue around London, and another eight are due to open within the next four years.
On Saturday, more than 300 cyclists rode through the capital in a "Tour du Danger" protest calling for the capital's roads to be made safer.
Cycling blogger Danny Williams said: "I think the superhighways should be made proper superhighways.
"I think it's a good idea, incredibly badly implemented and not very well thought through, and the Mayor needs to take responsibility for that.
A TfL spokesman said: "There has been an 18% fall in the number of cyclists killed or seriously injured on London's roads in the last decade, compared to the TfL's baseline figures from the mid to late 1990s."
No-one from the office of Mayor Boris Johnson was available for comment.