Various transportation analyses require the computation of the optimal strategy (or route) between two specific points on the transit network, and the detailed evaluation of its attributes. For instance, the calibration and use of disaggregate choice models require, for each individual considered, the explicit enumeration of the elements of the relevant choice set, as well as the values of their attributes.
In Release 4.0, two new modules have been added to the EMME/2 system:
5.34: Prepare Access / Egress Nodes for Individual Transit Trips
5.35: Analyze / Assign Individual Transit Trips
These two new modules have formerly been known as DISA, named after their use as an interface between DISaggregate (individual) data and Aggregate (network) data. These earlier versions of the two modules, then numbered 5.91 and 5.92, were not part of the standard EMME/2 system and were not included in the general distribution.
The two new modules provide a new framework in which individual trips that do not necessarily start and end at a centroid can be analyzed in detail.
The origin point and destination point of an individual trip are defined as their X-Y coordinates on the network plane. In this case, module 5.34 can be used to automatically select the set of possible access and egress nodes through which the origin and destination points are connected to the transit network. The maximum distance and / or the maximum number of nodes can be specified.
If the trip ends are defined at network nodes, or if the access and egress nodes are specified manually, module 5.34 is not needed.
Module 5.35 computes the optimal strategy to reach the destination coordinates from the origin coordinates, using the sets of access and egress nodes entered along with the coordinates. The necessary input data can be entered using batch input or through an interactiv dialog.
The computation of the strategy requires the computation of the access time from the origin coordinates to each access node, as well as the egress time from each egress node to the destination coordinates. The computation of these times is based on Euclidian distances and a user specified access / egress speed.
A logit approach with a clip-off threshold is used to compute the spreading of the trips among the different access nodes. This allows to fine-tune the spreading from using the nearest access node only (very high dispersion parameter) to giving equal weight to all access nodes (dispersion parameter zero).
The strategy is computed using the same preparation parameters as in module 5.11 to specify the traveler's behavior. The volume associated with the trip is assigned on the subnetwork composed of the selected links and transit line segments.
The output of module 5.35 is, for each trip, a report and / or a punch file containing the strategy and the corresponding time components or attributes: impedance, in-vehicle, waiting, boarding and auxiliary transit times, number of boardings, etc. All these components can be computed globally for all the transit or auxiliary transit modes, as well as for each mode individually.
Up to three user defined data can be associated with a trip. These data are simply "passed along" by modules 5.34 and 5.35 and they can be used to keep the associated socio-economic data, or other pertinent information about the trip, in the same data structures.
By default, module 5.35 does not alter the contents of the data base. The trip data, entered interactiveley of using batch entry, is processed locally to produce all the desired results in the form of a report and / or punch. However, if desired by the user, the so obtained transit volumes can also be accumulated onto the existing transit volumes of the current scenario. In this case, the newly computed transit times are also stored in the data base. Optionally, before assigning any individual trip in this way, the transit volumes can be initialized in module 5.35. This allows the user to "see a strategy", by first initializing the transit volumes and then performing an evaluation for a single trip. He can then use module 6.22 to plot the strategy (note, however, that the origin and destination coordinates of the trip do not appear on plots produced by module 6.22).
Modules 5.34 and 5.35 can be used for various purposes: