Athens, March 23 : Passenger and freight trains gradually resumed service in Greece, three weeks after an accident in the centre of the country that resulted in 57 deaths. Following a review of safety measures, operations will be fully restored in April, Panagiotis Terezakis, interim chief executive officer (CEO) of the Hellenic Railways Organization (OSE), said after the first train departed from Athens' central railways station, the Greek national broadcaster ERT reported on Wednesday. "We will do everything humanely possible to regain the trust of travellers, given that the railway is the most environmentally friendly mode of transport," he added. The government has pledged an in-depth investigation into the causes of the head-on collision of a passenger train with a freight train on February 28, as well as an upgrade of the rail network, Xinhua news agency reported. Until modern safety systems are installed, trains will run at slower speeds along specific parts of the network and staff numbers will be increased, Terezakis said. "There will be two stationmasters (at each station) and two drivers on each train," Ioannis Kokkinakis, stationmaster at Athens' central railway station, told journalists on Wednesday. On the night of the accident, one stationmaster was on duty at the nearest railway station. He and three other rail workers have been charged with manslaughter through negligence. The suspension of the operation of freight trains has not caused significant problems for Greek enterprises so far, but the operation of a safe and reliable rail network is of critical importance, Giorgos Karanikas, President of the Hellenic Confederation of Commerce and Entrepreneurship (ESEE), told Xinhua on Wednesday. Rail connection between Greece's ports and Europe's key markets is essential, as this is also the most cost-effective mode of transport for goods, he said. /IANS