Zagreb has an extensive tram network with 15 day and 4 night lines covering much of the inner- and middle-suburbs of the city. The first tram line was opened on 5 September 1891 and trams have been serving as a vital component of Zagreb mass transit ever since. Trams usually travel at speeds of , but slow considerably during rush hour. The network operates at the curb whereas on larger avenues its tracks are situated inside the green belts.