The network of buses, trams, metro and trains covers the whole city from 5.30am to around midnight, and night buses take over until about 5am, covering the main routes. The metro only has two lines, but is the easiest and fastest way to get around. The bus service is cheap and reliable, albeit slow due to traffic congestion. Tickets cover all forms of transport and must be pre-purchased and validated at the start of every journey; there are daily tickets valid for unlimited rides, or standard tickets that allow for any bus or metro ride within a 75 minute time frame. Taxis are notoriously expensive and display a list of surcharges. The historic centre of Rome is compact and manageable on foot, and most of it is closed to normal traffic. Driving in Rome is an experience to be avoided.