Dozens of passengers line up in single file along the platform in the dead of night, ready to gather their luggage and pile into the ageing railway carriages.At the small railway station in Nampula, in northeastern Mozambique, the 4:00 am train to Cuamba in the north west is more than full, as it is every day, to the detriment of those slow to board and forced to stand. In recent years, the government in Maputo has made developing the train network a priority as part of its economic plan. But mounting public debt has meant that authorities had no choice but to cede control of the project to the private sector.Seconds before the train - six passenger coaches coupled between two elderly US-made locomotives - leaves Nampula station, the platforms are already entirely empty. No one can afford to be late.Inside, the carriages remain pitch dark until the sun rises as the operator has not installed any lighting.A blast of the horn and the sound of grinding metal marks the train's stately progress along the 35km line to Cuamba - more than 10 hours away.Five or six passengers cram onto benches intended for four without a murmur of complaint.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook"The train is always full," said Argentina Armendo, his son kneeling down nearby. "Lots of people stay standing. Even those who have a ticket can't be sure of getting on. They should add some coaches!"'Enormous growth potential' "Yes, but it's not expensive," insists the conductor Edson Fortes, cooly. "It's the most competitive means of transport for the poor. With the train, they are able to travel."Sitting in a vast, ferociously air-conditioned office Mario Moura da Silva, the rail operations manager for CDN, the company operating the line, appears more concerned about passenger numbers as a measure of success than perhaps their comfort.In 2017, its trains carried almost 500,000 -- a 265-percent increase on a year earlier."Passenger traffic isn't profitable but it's a requirement of the contract with the government," said Moura da Silva."It's not that which earns us money, it's more the retail," he added, referring to the company's commercial operation, which has grown by 65 percent in a year.Brazilian mining giant Vale, which owns CDN along with Japanese conglomerate Mitsui, began its Mozambican rail venture in 2005.Having won a contract to run the concession from the government, it restored the former colonial line, which linked its inland coal mines with the port at Nacala.It now operates a network of 1 350km following an investment of nearly $5 billion."The growth potential is enormous," said Moura da Silva.Rail corridors Mozambique's government is eyeing the project as a bellwether for the industry."We have made infrastructure one of our four investment priorities," said Transport Minister Carlos Fortes Mesquita. "Thanks to this investment, the country recorded a strong growth in the railway sector."Eight new "rail corridor" projects are now under way in Mozambique, all funded with private capital, as the state grapples with a long-standing cash shortage.The government has been engulfed in a scandal linked to secret borrowing by the treasury, which is juggling debt amounting to 112 percent of GDP.As a result, a handful of large companies, attracted by Mozambique's vast mineral wealth, have taken the lead in developing the country's rail infrastructure.But it is unclear if their interest in the sector will continue in the long-term.Until the coal runs out? "Today the Nacala line only exists because of coal. But once the mine closes, who will be able to justify continuing operations?" asked Benjamin Pequenino, an economist at the University of Cape Town in South Africa."The private sector won't continue to invest if it knows it will lose money," he said.But in the absence of any alternative, former parliament speaker Abdul Carimo accepts that public-private partnerships are the least worst option.Carimo, who remains close to the ruling party, now heads up the "Zambezi Development Corridor".The scheme is managed by Thai group, ITD, and plans to build 480 kilometres of track between Macuse port and the coal mines at Moatize for a price tag of $2.3 billion.Carimo, who closely follows developments on the project, has vowed that "his" line will not only be used to carry minerals but will stimulate activity across the region it serves."I hate coal but I want this infrastructure to relaunch agriculture in Zambezi province," he said, adding that the region was "one of the richest in the country in the 1970s".