Network datasets are well suited to model transportation networks. They are created from source features, which can include simple features (lines and points) and turns, and store the connectivity of the source features. When you perform an analysis using ArcGIS Network Analyst, the analysis always happens on a network dataset.
A network dataset models the street network shown in the graphic below. The graphic highlights that one-way streets, turn restrictions, and overpasses/tunnels can be modeled. The analyses that are performed on the network, such as the route from stop 1 to stop 2, respect these and other network dataset properties.