Passengers in Croydon and Crystal Palace can now take advantage of full evening and weekend services on the new East London Line.
The line connects Dalston Junction in the north to West Croydon, New Cross and Crystal Palace in the south.
The route, which is a part of London Overground network, is the first phase of a £1bn extension of the line.
Transport for London said trains would run every 15 minutes on the New Cross, West Croydon and Crystal Palace branches of the line.
Trains will run every five minutes between Dalston Junction and Surrey Quays.
It predicted 40m passengers a year would use the line by 2016.
An extension of the line to Clapham Junction should be in place by 2012.
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