Attributes for calculating costs as a basis for path selection

Time interval for edge travel times in path search

Time interval of which the smoothed edge travel times shall be used:

• Same time interval, previous simulation run: Select this option for equilibrium assignment or for stochastic assignment (according to Kirchhoff). Always select this option when using equilibrium assignment (Attributes for path selection).
• Previous time interval, same simulation run: May result in less iterations to find paths in dynamic assignment and can thus speed up dynamic assignment. Vehicles respond faster to temporary queues. Do not select this option when using equilibrium assignment.

Cost for path distribution with Kirchhoff

Calculation procedure used as a basis to calculate costs for path selection if you have selected Stochastic assignment (Kirchhoff) or Equilibrium assignment for the distribution model. Existing volumes Volume (old) are not taken into account:

• Sum of edge travel times: The cost calculation is based on the smoothed travel times of the edges.
• Measured path travel times: The cost calculation is based on the smoothed travel times of the paths. If a path has no travel times yet, the sum of the edge travel times is used for this path.

For links with multiple lanes, the Measured path travel times option produces more accurate results than the Sum of edge travel times option: In both cases, Vissim determines the average travel times on the edges of the paths. However, the average edge travel time is less significant when travel times on an edge before a node strongly differ for different following edges, e.g. because right turn traffic in the node is congested but straight-on traffic is flowing. Therefore, Vissim does not use the sum of the average edge travel times when using option Measured path travel times, but the smoothed total travel time of all vehicles that reach the destination parking lot if at least one path travel time is available from a previous simulation run. In an overloaded network, it makes sense to use measured path travel times only, as the total of estimated edge travel times in congested areas may result in completely unrealistic total times.

Smoothing method

Selecting smoothing method for travel times:

• Exponential smoothing with smoothing factor: Value range 0.01 to 1, 1.0 = no smoothing, default value 0.20. If on the Choice tab, for Path choice model, you selected Equilibrium assignment, enter 1.0 (Selecting exponential smoothing of the travel times), (Attributes for path selection).
• MSA-method (method of successive averages), so far: If a dynamic assignment has been performed and as a result the cost file *.bew is saved, enter the number of iterations used to create the *.bew file. Default value 1 (Selecting the MSA method for travel times)

In the Files tab, the Store costs option must be selected. If the Write evaluations option is not selected, the smoothing of travel times is not performed. Instead, for each simulation run, the costs listed in the cost file *.bew are used.

The smoothing method is not relevant if you have selected equilibrium assignment (Attributes for path selection).