General cost, travel distances and financial cost in the path selection

The path selection depends on the following factors:

• Travel time
• spatial length of the paths
• financial cost on the paths, for example for toll

In contrast to travel times, the spatial lengths of the paths and the financial costs do not depend on the traffic conditions. Thus the spatial lengths of the paths and the financial costs do not need to be determined by simulation but can be read directly from the network model.

To account for these three factors in path selection, for each edge the so called general cost is computed as a weighted sum:

General cost = a • travel time + b • travel distance + g • financial cost + Σ surcharge 2

Where:

• The Cost Coefficients are entered in the attributes of the vehicle type (Defining path selection behavior with general cost function):

• a for travel time
• b fortravel distance
• g for link costs

• Avoid coefficients smaller than 0.01. Very small values may lead to significant computational inaccuracies. This is because when Vissim searches for the shortest paths, it uses rounded integers of the generalized costs of edges for performance reasons. It is best to use the default value 1 for both of the coefficients Journey time and Cost. This way you can always think of the generalized costs as in seconds. The additional costs per km and the values of the attributes Surcharge 1 and Surcharge 2 for the links are also given in seconds. The coefficient Distance then states how many seconds of additional journey time are added for each meter of distance.

• Cost coefficients are specific to vehicle types. This allows the modeling of driver groups with different path selection behaviors, with different time, path and money determinants (Defining simultaneous assignment).
• The travel distances are determined from the geometry of the links.
• The financial cost of an edge is the sum of the costs of all links that are contained in that edge.
• The cost is computed by multiplying the cost rate per meter specified in the link by the length of the route which is contained in the edge. If for a link the Surcharge 1 attribute contains a value, it is added (Attributes of links).
• Link attribute Surcharge 2:: Additional surcharge for the link. Is added to general link costs without weighting (Attributes of links).