The nested logit approach, which underpins the Nested Demand Model, represents behavioural choices (typically trip distribution, mode choice and time of the day choice) in hierarchical model structures. The appropriate hierarchy of choices must be determined by the relative sensitivities to the utilities of travel. Choices made higher in the hierarchy act as constraints on those made later further down the hierarchy. The calculation of utilities starts at the bottom of the hierarchy. The resulting log sums are passed on to the next level in the hierarchy adding one more choice at each level on the way up the hierarchy.
This type of demand modelling is standard practice in the UK and is currently being used by the DfT’s own National Transport Model with PTV Visum. This is therefore an ideal approach for modelling that is in line with DfT’s and WebTAG recommendations.
Over the course of the training, you will define some procedure steps yourself within the framework of this exercise. The steps and the context within the calculation will be explained. Afterwards we will calculate the demand by using the absolute model form, i.e. the calculation is based on demographic and structural data of zones.
