Turn Penalties at an Intersection
The above table represents the turn penalties for a typical intersection between two streets represented as Node A. From each direction, there are three possibilities; going straight ahead, turning left of turning right. This intersection consequently has 12 turns, each having a specific attributed penalty. Straight flows (1-3, 3-1, 2-4, and 4-2) are assumed to have no "turn" penalty. Right turns (2-1, 1-4, 3-2 and 4-3) are assigned one standard turn penalty, which can be represented as an average number of seconds. Left turns (1-2, 4-1 and 2-3) are assigned two standard turn penalties. One left turn, 3-4, is prohibited by a traffic sign (negative value). With this information, a network data model has all the required information to handle routing at this intersection.