A Turn Function is used in EMME/2 to describe the time it takes to make a turning movement from one link to another. By default, EMME/2 assumes that no turns (except U-turns) are prohibited, and that there is no time delay associated with any particular turning movement.
A Turn Function is described by 4 parameters: Function Number, UP1, UP2, and UP3. How these items are used is dependent on the implementation of a particular EMME/2 model, and are described fully in the EMME/2 documentation. The 2.11 Toolbox also adds a fourth item: Project Number. This item allows the user to associate a turn function with a particular Project, so that the Turn Function will be included in a particular simulation network only if its associated project is.
For a technical description of how Turn Functions are stored in the 2.11 Toolbox, please refer to The Turns Database.