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Next: Line Specific Boarding Times Up: EMME/2 NEWS 16 June 1994 Previous: ``Cutoff'' Operator for Additional Options

 

Additional Options for Transit Assignment

Ever since the introduction of the additional options for the auto assignment, transit modelers have been longing to get access to a similar feature for the transit assignment. While it was always possible -with some work-arounds- to find the O-D pairs which are using or not using a certain facility, there was no way to obtain the precise part of the demand, nor to reliably compute additional attribute matrices, such as a true transit distance matrix.

Transit assignment users will be happy that Release 7 does provide this long awaited new feature. Given the very different nature of auto and transit assignment, it is not possible, nor desirable, to implement the additional options for transit in exactly the same way as it is done in the auto assignment. So, before discussing the actual implementation, let us look again at the main differences between the two assignment models:

figure185

From the above comparison, it follows that the implementation of the additional options for transit has to be quite different from the one for the auto assignment. Assuming that the reader is already familiar with the general concept of the additional options for the auto assignment, here is a summary of the main differences for the transit implementation of the similar functionality:

It is, of course, not possible here to go into all the technical details of the implementation of the additional options for transit. For in-depth technical information, please refer to the corresponding pages in the Release Notes and the EMME/2 User's Manual. Instead, let us look at some interesting applications which become possible with this new development:

To carry out an additional options assignment, module 5.11 is used to prepare the scenario for a transit assignment as usual. At the very end of the standard assignment preparation dialog, the following question has been added:

   Perform additional options assignment?
When answering ``no'' to the above question, module 5.11 is left and the scenario is ready to be assigned. Thus, only a minimal change is needed to update existing transit assignment macros to be compatible with this new development: it suffices to add a ``no''-line just after the line containing the boarding time weight (which is usually just before the call to module 5.31).

If the additional options are activated by answering ``yes'' to the above question, a dialog is generated, in which the user is first prompted to specify the additional boarding, invehicle, alighting and auxiliary transit attributes which will be used to characterize the strategies. Only those attributes which are pertinent for the desired analysis have to be specified, non-specified attributes defaulting to zero. Also, full attribute inheritance is implemented for the additional attributes, e.g. if a transit line attribute is specified as the boarding segment attribute, the value for each line will automatically be copied to all its transit segments. The dialog proceeds then to prompt the user for the part of the strategies to be retained during the assignment, the path and sub-strategy combination operators and the threshold values for determining active strategies. Finally, the user can choose to save two result matrices: the additional strategy attribute matrix contains the values obtained by applying the path and sub-strategy combination operator to the additional attribute values along the strategy, and the active transit demand matrix contains that part of the demand which satisfies the given condition, i.e. the demand which corresponds to the retained transit volumes.

The following example illustrates the new dialog in module 5.11 for a select line analysis. The plot below shows the resulting additional volumes, i.e. the volumes of all trips using the selected line.

Perform additional options assignment? yes

Enter: Additional boarding attribute= @selin
T: @selin  select line 24                            94-05-22 08:02
Enter: Additional invehicle attribute= 
Enter: Additional alighting attribute= 
Enter: Additional auxiliary transit attribute= 

Select: Retained part of strategies
        1= Complete strategies
        2= Minimum attribute sub-strategies
        3= Maximum attribute sub-strategies
          3

Enter: Path operator(+)= .max.

Enter: Lower, upper threshold for active strategies= 1 1

Matrix to hold additional strategy attributes (optional)
Enter: Matrix( mf )= 

Matrix to hold active transit demand (optional)
Enter: Matrix( mf )= line24
mf04: line24     partial demand using line 24             (94-04-30 11:43)
Change header information? no

select line plot


next up previous
Next: Line Specific Boarding Times Up: EMME/2 NEWS 16 June 1994 Previous: ``Cutoff'' Operator for Additional Options


Heinz Spiess, EMME/2 Support Center, Thu Jun 6 14:58:10 MET DST 1996