although there are still examples of stops where passengers must board from street level. Zürich's trams are single-ended, with doors on only one side, although Forchbahn trains are double-ended and double-sided. In consequence all terminal locations are equipped with turning loops, and all tram stops are to the nearside of the tram. Depots and workshops Zürich's tram fleet is kept in the five operational depots of Hard, Irchel, Kalkbreite, Oerlikon and Wollishofen, together with a permanent way yard at Hardturm. Whilst these depots have the capability to undertake minor maintenance, heavier maintenance is the responsibility of the VBZ's central workshop at Altstetten. This is connected to the tram network, and also has a rail connection to the Swiss Federal Railway system, allowing the delivery of infrastructure items and vehicles by rail. In addition to the above depots and workshops, two other former tram depots, at Burgweis and Wartau, are also still connected to the tram network. Burgweis depot now houses the Tram-Museum Zürich main collection, whilst Wartau is used as a workshop by that organisation. The rail connections permit the occasional operation of preserved trams on the VBZ network. Tram fleet As of 2012, the VBZ owns 313 tram vehicles, which between them cover over 16 million vehicle-kilometres per year. All regular public services are covered by 289 vehicles of two basic classes, with the remainder of the fleet made up of a number of assorted works vehicles, including some used for the cargo tram service, and heritage vehicles. The heritage fleet sees occasional use on special services. The tram fleet comprises the following vehicles: Fares and tickets Like the rest of the VBZ network, Zürich's tram network operates on a proof-of-payment system. All tram stops are equipped with ticket machines, and passengers are required to purchase a ticket before boarding the vehicle. Passengers may board through any door and are not required to show tickets on boarding. Instead, tickets are randomly checked by roving teams of fare inspectors, and fines are imposed on passengers found without one. Tram services are operated within the fare and ticketing system provided by the cantonal public transport authority, the Zürcher Verkehrsverbund (ZVV). This system covers the whole of the canton of Zürich and thus covers travel on other modes and services, provided by many other operators, and includes the Zürich S-Bahn suburban rail network. Free transfer is permitted between different vehicles, routes, modes