Several users have expressed the need to be able to preload turning movements with exogenous additional volumes. This need arises when studying detailed subarea traffic (e.g. shopping center impact) where regional through traffic is considered constant and given. Without the possibility of preloading additional flows to turning movement, it is not possible to represent correctly total turning movements on intersections.
In principle, there is no problem having additional volumes on turns. In fact, they already exist in the current release, containing, if the user has chosen so in module 5.11, the turning volumes associated with the transit vehicles. The problem is more on where and how to enter these additional volumes exogenously, without penalizing the majority of users that do not need this feature. Thus, we were looking for an elegant way to solve the problem without adding new internal files that a) take up space on the disk and b) would make old data bases incompatible with the new release.
Well, after some hard thinking, we came up with such a solution. Besides being upward compatible with current data bases and not requiring any extra space in the data base, it also extends one of the basic concepts of EMME/2, that of the user defined data. Just as for nodes, links and transit lines, it is now also possible to enter up to three user defined numeric data items for each turn. These are entered in module 2.31, interactively or in batch mode, by adding them after the penalty code on the turn input lines. Note that items not specified default to zero and that only values different from zero are actually stored in the data base. The values are stored right in the intersection definition file (for the technically interested: int file 41, see appendix C of User's Manual). Each non zero item will take up one entry in that table. This means that if more user data items are defined, the total number of definable turns actually decreases. In practice this should not cause any problems, since the size of the intersection definition table is usually not a limiting factor. (The size of the turn table, however, is often a critical dimension, but it is not affected by the number of user defined data items on turns.)
The existence of user defined turn data, implies two other changes in the EMME/2 system. First, when plotting intersections using module 2.31, the user has now the choice of displaying either the penalty functions or one of the user defined data items. Second, when preparing an auto assignment with module 5.11 and using additional demand from user data, the user will be prompted for link and turn data items. Values 1 to 3 imply the corresponding data item, a 0 implies that no additional data is copied from user data for this class of elements (links or turns).