The Trans-Persian Railway Opening

“The lots conferred to Impresit were among the most difficult to execute”, says Andrea Filippo Saba, a University of Florence researcher, in a 1995 academic paper. Four of the lots were in the north where Impresit had to build an access ramp to a tunnel under Gaduk Pass in the Alborz mountain range. It climbs 1,200 metres in less than 50 kilometres. With an average gradient of 26%, it rises from 1,000 metres above sea level to 2,200 metres.