Turn Attribute for Additional Options Assignment

The path attribute (and with it the path selection mechanism) of the additional options auto assignment of EMME/2 has so far only been based on the values of the specified additional link attribute.

In the new release, an additional turn attribute can optionally be specified along with the additional link attribute. This opens the new possibility of computing path attributes which are based on turn attributes, and thus makes it possible to base path selections explicitly on the traversed turns and to compute additional O-D attribute matrices which include turn information.

This new feature is activated in module 5.11 by choosing the new option 7 of the question which selects the source for the additional attributes, which now reads:

   Select: Source for additional attributes
           1= link user data UL1
           2= link user data UL2
           3= link user data UL3
           4= link length
           5= none (no additional path attributes calculated)
           6= link user data, length or extra link attribute
           7= additional attributes on links and turns

If a link and a turn attribute is specified, the path attributes are computed by combining all link and turn attribute values along each path with the specified path operator.

When computing traversal matrices (using the special path operator traversal) in- and out-gates can now be specified at the turn level as well.

Here are some examples of possible applications for which the new additional turn attributes are useful:

• ``Select turn'' type analyses. Even though the volume on a single turn could already be analyzed using only a link attribute which flags the incoming and outgoing links of the turn, for answering any more complex turn related questions, the use of the turn attribute is essential (such as e.g. the computation of all trips which do U-turns).
• Compute turn delay matrices or toll(cost) matrices when tolls are located on turns.
• The current implementation of demand adjustment procedures (such as the gradient method implemented in macro demadj.mac) are limited to link counts. With the introduction of additional turn attributes, such procedures can be extended to allow for demand adjustments based on turn counts as well.
• For a full implementation of the system optimum assignment for networks using general turn penalty functions, additional turn attributes are needed for the computation of the (non-marginal) impedance matrix.
• For time-based cold start analyses (implemented using the cutoff path operator), the turn delay at nodes can now be accounted for as well.