Turkey's long-awaited 8.6 billion lira ($4.1 billion) high-speed train link between Istanbul and Turkish capital Ankara has begun operating from Istanbul's Pendik station.The high-speed service, which reduces the travel time between Istanbul and Ankara to three-and-a-half hours, will be free of charge for the first week of the operation.Train driver Özdemir Sırmagül told Anadolu Agency on Sunday the 409-passenger capacity train was full as a result of intense interest and the fact most Turkish citizens were on holiday for the feast to mark the end of Ramadan, creating an increased demand for transport.Twelve trains will run in the first week, Sırmagül added.One of the first passengers, Gülsüm Demirtaş, said she had got five tickets for her family and they were going to visit Ankara for the traditional eid holiday.Another passenger traveling in business class, Sukran Kinik, thanked those involved in the rail project.- Discounted ticketsTickets for the Ankara-Istanbul service are priced at 70 lira, which children aged under seven are free of charge. Children between the ages of seven and 12 pay 35 lira.Discounted tickets are also available for students (55 lira) and senior citizens (35 lira).The line was inaugurated by Turkey's Prime Minister Recep Tayyip Erdoğan on Friday.The high-speed service was first introduced in 2009 between the capital Ankara and Eskisehir to the west.The latest line links Eskişehir to Istanbul-joining Turkey's political and financial capitals.- Expansion plansThe original track has proved immensely popular with Turkish passengers, carrying 15 million since its launch, Turkish State Railways said.An estimated 7.5 million passengers are expected to use the new line.The new addition to the country's high-speed network means 1,420km of track can now carry the faster trains.There are plans to grow the network to 3,500km by the centenary of the Turkish Republic in 2023.A link between Ankara and the Aegean city of Izmir-Turkey's third largest-is high on the agenda as the network expands to 25,000km of track.Eventually, 17 cities will be connected by high-speed lines, servicing more than half the country's 77 million population.Turkish State Railways announced in January that it would invest almost half of its 2014 budget-1.8 billion lira ($860 million)-in high-speed train projects.