and rules were observed. The Transport Accident Investigation Commission may also inquire into selected accidents and incidents to determine the circumstances and causes and help prevent similar occurrences in the future. Modern signalling, train detection and communications systems, as well as an overall decline in rail passenger traffic, has greatly decreased the number of fatal accidents occurring on New Zealand's railway network. New Zealand's most serious rail disaster occurred on Christmas Eve 1953, during the visit of Queen Elizabeth II, when a lahar washed away the bridge in the Tangiwai disaster. 151 people died when the bridge collapsed as a Wellington-Auckland express passenger train was crossing it. The next most serious accident was the Hyde railway disaster of 1943, when the Cromwell - Dunedin express derailed after travelling at excessive speed. 21 people died. The driver was later found to have been intoxicated and was jailed for manslaughter. Heritage rail Heritage mainline passenger services Four heritage rail operators own and operate their own carriage and mainline-certified steam or diesel locomotive fleets. These are the Railway Enthusiasts Society, Steam Incorporated, Mainline Steam Trust and the Otago Excursion Train Trust (Dunedin Railways). These groups have operated special excursion trains on the national network since 1978, and have been allowed to use suitable locomotives to haul these trains since 1985. Heritage and museum railways About 60 groups operate railway heritage lines or museums, almost all members of the Federation of Rail Organisations of New Zealand. They include street tramways and bush tramways as well as railways. Large-scale rail preservation in New Zealand got underway in the 1960s when many steam locomotives were withdrawn and branch lines closed. Current operations of the heritage railway type include the Kingston Flyer, Glenbrook Vintage Railway, Bush Tramway Club, Waitara Railway Preservation Society, Weka Pass Railway, and Dunedin Railways. Dunedin Railways is a Council-controlled organisation (CCO) 72% owned by the Dunedin City Council and runs the Taieri Gorge Limited which is in length, and various other services around Dunedin and Otago. All other lines are operated by voluntary societies. The Weka Pass Railway at is the most lengthy of these. The Bay of Islands Vintage Railway is in length, but is in poor condition; having operated its first trains through Kawakawa since operations ceased in 2000 for two weeks from 3 July 2007, the Society is now working on rehabilitating the track between Kawakawa and Opua. In popular