The first section of the East London Line in the UK has been officially opened by London Mayor Boris Johnson.
Costing £1bn ($1.5bn), the project was delivered on time and on budget, according to Transport for London (TfL).
A full service is expected to begin on 23 May with trains travelling from Dalston Junction in the north of London to West Croydon in the south, via the City and Docklands.
The line will be serviced by a fleet of 20 Class-378 Electrostar trains with a capacity of 494 passengers each.
TfL expects the line to be used by 100,000 passengers a day during the first year and has ordered a further 13 trains, which will join the fleet by 2012, to deal with increasing demand.
It has been built on and extends the old East London line and features four new and 14 refurbished stations.
The line is expected to provide a key component of the 2012 Olympic and Paralympic Games transport network.