The TT3 model represents a model system which is primarily aimed at investigating large-scale EU projects. Moreover, even at the aggregated European level it is primarily aimed at the benchmarking of different projects.
The TT3 model system consists of three main sub-models for:
- Passenger demand
- Freight demand
The passenger model includes two main parts:
- A short distance model for trips shorter than 100 km
- A long-distance model for trips longer than 100 km
The models cover all relevant trip purposes across 42 countries in Europe as well as connections to the other parts of the world. The models deal with choice of mode, destination choice and frequency choice. The methodology applies non-linear utility functions in order to address scaling effects properly. There are two main parts in the freight model: the trade model and the logistics model. The trade model delivers production-consumption matrices for future exogenous growth (scenario inputs), whereas the logistics model then (using the pivoting approach) generates matrices of freight flows between origin and destination zones by mode and commodity type. These can then in turn be used to generate the final outputs (e.g. impacts of policy measures of the model system).
The assignment model consists of two parts. The first part concerns the passenger assignment models while the second part concerns the various freight models that are fed to the chain choice model. The demand models and the assignment models are iterated and after a sequence of iterations equilibrium is obtained. The equilibrium corresponds to a situation in which the demand is balanced with the supply, hence congestion effects are internalized in the demand and demand is internalized in the supply. The Figure above illustrates the overall structure of the TT3 model system and how the different sub-models are linked.
The demand part of the model is divided between a passenger model and a freight model. Both models provide demand in the form of matrices which are then input to the assignment model from which LoS variables are calculated and used as new input in the next iteration. From this process, the final origin-destination matrix is obtained together with the final equilibrated LoS. These are then used in the impact assessment.