The BTS extension from Saphan Taksin station to Wong Wian Yai is the first Skytrain route to venture across the river to Thon Buri.
For years, Bangkok commuters have faced a rush hour nightmare on the way to work or school each morning. That nightmare lasts longest in Sathorn, the capital's central business district - and its most congested.
It should help ease the traffic jams along the Sathorn Road at the King Taksin Bridge route, the most gridlocked road in Bangkok.
Around 2,000 vehicles are expected per hour during rush hour after the BTS extension opens, compared to almost 15,000 vehicles currently.
Prime Minister Abhisit Vejjajiva was at the launch ceremony to wave off the first train. The BTS extension is expected to boost the estimated 400,000 Skytrain journeys made every day by around 30,000 to 50,000.
A campaign is being launched to encourage parents who usually drive their children to schools in Sathorn area to use the Skytrain instead. Parking space has been increased near the newly opened stations and shuttle buses will ferry passengers to stations
The extension is a huge boost for Thon Buri commuters who have to cross the Chao Phya River to get to work.
The Skytrain link to the rest of the city means that Thon Buri has become Bangkok's new hot property, and condominiums have mushroomed close to the extension's two stations to meet demand.
