Getting around in Des Moines is simple thanks to the Des Moines River, which flows through the centre of town and acts as an orienting landmark. Streets east of the river are prefixed with 'East', and those west of it have 'West' or no prefix at all. The streets are easy to navigate. However, driving in winter is not something to be attempted lightly, as snow and ice make conditions difficult for inexperienced winter drivers. The Des Moines Area Regional Transit (DART) system has a network of buses covering most of the city, and service that runs into the evening. There are several taxi companies available 24 hours, but cabs must be called in advance.