The main line on Africa's fastest railway opens Tuesday, shuttling commuters from Johannesburg to Pretoria at speeds up to 160 kilometres (100 miles) an hour - if they're willing to leave their cars.
The Gautrain has run between Johannesburg's Sandton business district and the airport since just before the World Cup last year, but the new line connects South Africa's economic hub with the capital city, bypassing the country's most gridlocked highway.
"The Johannesburg area is one of the 10 most congested cities in the world. Sometimes it takes more than two and a half hours to drive 60 kilometres," the distance to Pretoria, said Barbara Jensen, spokeswoman for the project.
"We have to get people moving."
The Gautrain will slash travel time to just 27 minutes, gliding past traffic jams that have grown as suburban sprawl enmeshed the two cities together.
Together they are home to about six million people, in the tiny province of Gauteng, that accounts for 40 percent of South Africa's economy.
The cities are already served by a network known as Metrorail, a service mainly for the working class. Even the Metrorail express train takes three times as long to travel between the cities, stopping in townships along the way, but for a fare about half of Gautrain's 49 rand ($7, five euro) tickets.
Gautrain doesn't serve the region's townships, but links key business and shopping districts - areas where the car is currently king.
The final six kilometres of the line, expected to open by the end of the year, will connect Johannesburg's Rosebank business district to the city centre. That leg was delayed because of water seepage in the tunnel, which contractors are still working to resolve.
When that link opens, the Gautrain will run to Park Station, Johannesburg's busiest transport hub.
--'The trains will be full'--
While South Africa is widening highways to ease chronic traffic jams, it's also preparing to impose tolls, angering drivers but making the Gautrain's ticket price competitive.
The new railway was built by a consortium called Bombela, which includes French giant BTP Bouygues and Canada's Bombardier, the world's railway leader.
RATP Dev, a subsidiary of the firm that runs Paris's mass transit, has a 15-year contract to run Gautrain.
The entire project cost 25.4 billion rand, but Bombela is already warning of overruns, reportedly running to billions of rands.
It's a huge amount for a country where one in five people still don't have electricity, making Gautrain a lightning rod for criticism.
"I do not dispute the fact that the train is expensive," Jensen said. "In South Africa, we have a lot of challenges with regards to transport, and especially public transport. Perhaps we should have started 20 years ago."
The airport link, which slashed travel times to 15 minutes, is already a success, said Laurence Le Blanc, RATP Dev's head of international business.
"We're good on all the performance indicators, in terms of quality of service, on-time service, and for security, which was a major concern, it's encouraging," she said.
"We have shown that there can be a train that's good quality, efficient, high-performance, and safe."
Didier Lescloupe, head of testing for RATP Dev, predicts plenty of demand.
"Lots of passengers are expected, and the trains will be full," he said.
"We may even run more trains than called for in the contract."
Feeder buses will run through neighbourhoods around most stations, trying to ease people out of their cars.
"It's a cultural revolution," said Alain Esteve, another RATP Dev official.
And there's already talk of new routes for Gautrain, possibly toward the historic township of Soweto.
"People are very happy," Jensen said. "They are so happy to the extent that they are asking for extensions to other parts of Gauteng."
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