All Routemaster buses will be withdrawn by 2006
More than 100 of London's iconic Routemaster buses will finish their final journeys on Friday after 50 years on the city's streets.
Enthusiasts are calling it "Black Friday" as the old-style "hop-on, hop-off" vehicles on routes 9, 73 and 390 are replaced.
All Routemasters are expected to be taken off the bus network by 2006.
Transport for London (TfL) says bendy buses carry more people, are cheaper to run and have better disabled access.
But at 18 metres (59 feet) long there are concerns bendy buses on the three routes at the heart of London's busiest shopping district, could create more congestion.
A number of events are being held to mark the Routemaster's "retirement" on the three key routes through Oxford Circus and Piccadilly.
Routemaster fan Andrew Boath told BBC London: "The tragedy is, they will never build a bus like it again, it was a one-off.
"If I want to jump off at a junction, I can do...with the modern ones you can't, you are trapped in there."
Supporters say the buses are still the best way of moving crowds in London.
But Routemasters can only carry 73 passengers, compared to 120 on bendy buses, and TfL says demand for bus travel is growing at its fastest rate since 1945.
Mike Weston, of London Buses, said: "I think everybody involved feels that the time is right to move on and bring in more accessible buses.
"A lot more passengers are pre-paying before they get on the bus, so the need for conductors to collect fares has reduced over the last four years."
And not everyone is a fan of the old-fashioned buses.
Commuter David Phillips said the number 73 to work was "uncomfy, slow and noisy".
He added: "There's never room for things like luggage, pushchairs, there's no access for a wheelchair."
One more Routemaster route is due to be "retired" this year and the remaining seven next year.
But London mayor Ken Livingstone has said some will be kept for heritage and tourism purposes.