bus lines that have a number starting with 6 connect zona north with the zona west. bus lines that have a number starting with 7 and 9 connect rio de janeiro with neighboring towns such as nova iguaçu, niterói, and duque de caxias. bus lines that have a number starting with 8 only stay within the zona west. troncal lines are lines that connect various parts of the city to central areas - there is a total of 10 troncals that transfers passengers to some of the main streets of rio. buses in rio are generally safe, however depending on the route and the time of day, or night, buses can be unsafe to ride for people, specially for visitors who may not be as familiar with the city - it is best not to use buses late at night, and never display expensive items or electronics.