Carlos Nuzman, the President of Rio 2016, and Ricardo Teixeira, the President of the FIFA 2014 World Cup Organising Committee, took part in a special ceremony to celebrate the landmark.
They were joined by Rio Mayor Eduardo Paes.
The project, which involves a total investment of R$692.1 million (£256.4 million/$405.6 million), is designed to prepare the city’s highway system for the 2014 World Cup and 2016 Olympic Games.
Transoeste will have 30 Bus Rapid Transit stations, a trolley bus corridor with express lines and bus stops.
The start of the ceremony signalled by an explosion for the opening of the Grota Funda tunnel, one of the critical stretches.
The construction work is set for completion within two years.
With the construction of the Transoeste, journeys of people between Barra and Santa Cruz will be 150 per cent faster at peak times, benefiting thousands, claimed Nuzman.
"This project is one more demonstration of Mayor Eduardo Paes commitment concerning the guarantees given to the International Olympic Committee at the time of Rio´s candidature to the Games," said Nuzman.
"I am happy with this intervention, which helps the city welcome the Games and improves the population life quality."