A network is a system of routes. Routes are individual paths that are taken by transit vehicles. Routes include a spatial element—the streets and stops that are serviced along the way, and a temporal element —the time that the bus will arrive and depart from each stop or station.

Selecting a network structure is a complicated task, for which there is not a simple solution. There are, however, a few network structures that have become very common.

Grid networks are common in large cities. These systems tend to be centered on the central business district with few routes venturing far outside the central business district (CBD). Grid networks make extensive use of the existing roadways. Where traffic is heavy, deep within the CBD, one or more exclusive bus lanes may be required in order to provide buses with adequate freedom to move. Exclusive bus lanes increase the capacity of the system by reducing delays caused by interfering traffic, but the exclusive bus lanes also reduce the capacity of roadways to handle private traffic and parking.

Radial networks are also frequently found in modern cities. These systems contain linear routes from the CBD to outlying suburbs. Commuters who live in the suburbs and work in the central business district are well served by radial networks, but those who want inter-suburb transportation are not well served, unless there are direct lines connecting each of the suburbs. Exclusive bus lanes are occasionally included on radial routes as well.