from Palmerston North. The Northern Explorer to Auckland was discontinued in December 2021. Four electrified suburban lines radiate from Wellington railway station to the outer suburbs to the north of Wellington – the Johnsonville Line through the hillside suburbs north of central Wellington; the Kapiti Line along the NIMT to Waikanae on the Kapiti Coast via Porirua and Paraparaumu; the Melling Line to Lower Hutt via Petone; and the Hutt Valley Line along the Wairarapa Line via Waterloo and Taitā to Upper Hutt. A diesel-hauled carriage service, the Wairarapa Connection, connects several times daily to Masterton in the Wairarapa via the Rimutaka Tunnel. Combined, these five services carry 11.64 million passengers per year. Wellington is the North Island port for Cook Strait ferries to Picton in the South Island, provided by state-owned Interislander and private Bluebridge. Local ferries connect Wellington city centre with Eastbourne and Seatoun. Wellington International Airport is south-east of the city centre. It is serviced by flights from across New Zealand, Australia, Singapore (via Melbourne), and Fiji. Flights to other international destinations require a transfer at another airport, as aircraft range is limited by Wellington's short () runway, which has become an issue in recent years in regards to the Wellington region's economic performance. Infrastructure Electric power Wellington's first public electricity supply was established in 1904, alongside the introduction of electric trams, and was originally supplied at 105 volts 80 hertz. The conversion to the now-standard 230/400 volts 50 hertz began in 1925, the same year the city was connected to the Mangahao hydroelectric scheme. Between 1924 and 1968, the city's supply was supplemented by a coal-fired power station at Evans Bay. Today, Wellington city is supplied from four Transpower substations: Takapu Road, Kaiwharawhara, Wilton, and Central Park (Mount Cook). Wellington Electricity owns and operates the local distribution network. The city is home to two large wind farms, West Wind and Mill Creek, which combined contribute up to 213 MW of electricity to the city and the national grid. While Wellington experiences regular strong winds, and only 63% of Wellington Electricity's network is underground, the city has a very reliable power supply. In the year to March 2018, Wellington Electricity disclosed the average customer spent just 55 minutes without power due to unplanned outages. Natural gas Wellington was one of the original nine towns and cities in New Zealand to be supplied with natural gas when the