Route 9 will be served by the New Bus for London - also known as the 'Boris Bus' - which has a conductor and the same hop-on hop-off feature as the old Routemaster.
The route - which runs from Hammersmith to Aldwych will get 22 of the new buses from Saturday. 16,000 people use the route every day.
Route 9 joins routes 24 and 11 which are already run entirely with a fleet of New Buses.
Route 390 will become part of the exclusive group on 9 December.
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A lamp in the tower which houses Big Ben is to be switched off for the first time in more than 70 years.
Sir Bruce entertained audiences for more than seven decades.
Work in the tower will also pause over the bank holiday weekend.