The presidents of Brazil, Bolivia and Chile have agreed to build a highway by 2009 that will link the Atlantic and Pacific coasts of South America.
The three leaders hailed the deal as a boost to trade
Much of the route is already paved but the leaders agreed to invest a further $600m (£300m) to complete the road.
The highway is to run from Santos in Brazil to Arica and Iquique in Chile.
The meeting in the Bolivian city of La Paz was seen as a chance to improve strained ties between Bolivia and Chile and boost Bolivia's links with Brazil.
Bolivian President Evo Morales hosted the summit at which he and his counterparts from Chile and Brazil, Michelle Bachelet and Luiz Inacio Lula da Silva, agreed to build the east-west highway across South America.
The road will be some 4,700km (2,900 miles) long when finished, running from the port of Santos on Brazil's Atlantic coast, through Bolivia and on to Chile's Pacific ports of Iquique and Arica.
Ms Bachelet said the deal would promote economic prosperity in the region.
"We know we need to grow so that we really have the social policies that permit us to better the lives of our people," she said.
President Lula said there was much to be gained by the project. "Many people ask themselves how much this undertaking will cost. I ask myself how much did it cost us by not having done it before," he said.
The completed road is expected to boost trade, allowing greater access from Brazil to markets in the Asia-Pacific region.
The economy of land-locked Bolivia is expected to benefit significantly from the improved road network, correspondents say.
Mr Morales said the project was important for integration and cooperation, and said the planned highway would be "a vein that allows us to unite peoples from Chile, from Bolivia and from Brazil".
President Bachelet's visit to Bolivia was a rare trip to the country by a Chilean leader.
Ties between the two South American neighbours have been difficult since Bolivia lost its access to the sea in a 19th Century war with Chile.
Relations between Bolivia and Brazil suffered a more recent blow in 2006 when President Morales moved to nationalise his country's energy industry.
Brazil's state-run energy company Petrobras is the biggest investor in Bolivia's natural gas sector.
However, during his two-day visit, President Lula was expected to announce a resumption of Brazilian investment in Bolivia amounting to $750m.