Nested mode choice can be defined in a Nested demand procedure. It thus represents one step of the 4-step model with sequential calculation. The total demand (total demand matrix) per demand stratum is distributed to the transport modes defined in the network (for example car PrT, bus PuT), using mode-specific utilities (Image 61).
Image 61: Modeling based on model structure in Nested demand procedure decision tree
In the Nested demand procedure, the decision tree illustrated in Image 61 is defined through a model structure with the choice level mode choice. The modes at the leaf node must correspond to the modes defined in the demand model.
Leaf node utility can be specified through a formula of skims, demand stratum-specific parameters and constants. Nest node utility is computed during calculation of the Nested demand model (Nested demand model).
As a result, the procedure calculates a demand matrix for each leaf node and - optionally - for each nest node as well. The logsums calculated per nested node can be optionally saved to a skim matrix and used later for evaluations.
