VISSIM 5.30-05 User Manual

12 Dynamic Assignment
Without the Dynamic Assignment, routes for the simulated vehicles are
supplied manually using the network editor. The optional Dynamic Assignment
module however is designed to model the route choice behavior of
drivers, thus allowing to model networks without static routes and instead
using the specification of origin-destination matrices as flow input. In VISSIM
the assignment is done dynamically over time by an iterated application of
the microscopic traffic flow simulation.
The following terminology is used when referred to Dynamic Assignment in
this chapter:
► path and route are used as synonyms.
► cost in its exact meaning denotes financial cost, i.e. the component of
the general cost that is not travel time and not distance. But cost is often
used instead of general cost if the context allows for it.
► general cost is the weighted sum of travel time, distance and cost. The
general cost is what is used in the route choice model as the utility of the
routes to choose from.
► travel time of a route or an edge is the average time the vehicles need
to travel from the beginning to the end of the route resp. edge in the
current simulation.
► smoothed travel time is computed by exponential smoothing of the
travel times measured in the course of iterations. The smoothed travel
time is the one that is used in the general cost function.
► expected travel time is used if we want to express the difference
between the travel time that is used in the route choice model at trip
begin (that is the expected travel time) and the travel time that actually
can be measured after the trip is completed.
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