Current 4-step models are unable to meet the requirements of policymakersto forecast the effect of many of the new policy measures which they wishto implement (e.g. road pricing, peak spreading, parking). On the other hand there is intense interest in activity based models because they are policy-responsive. Most of the models in Europe are 4-step models and if they are to be migrated to an activity based modelling framework then this can either be undertaken by building a new activity based model from scratchor by migrating the existing model to an activity based model framework. Most of these models are in use, so migration is often the preferred option, with a requirement to complete the migration in stages so that the model can use the enhancements introduced at each stage in the migration process. To take full advantage of the activity based framework requires new data to be collected. However calibrating an activity based model with a 4-step model data provides a better model than the 4-step model calibrated with the same data. This study shows how to configure distribution and mode choice as a hierarchy of choices which are modelled with a set of nested choice models which can be calibrated with the same source data as was usedfor the 4-step model. It shows how this can be extended to include other travel choices including time period choice, time interval choice and parking choice, interfaced with the same highway and public transport assignment models as used for the 4-step model. Complex elements such as activity duration, which is dependant upon a range of characteristics such as the makeup of the travelling party can also be encapsulated within the model. If necessary a trip frequency model can be applied at the beginning of the choice hierarchy to provide sensitivity of the model to trip suppression and induced trip making in response to improved transport provision or worsened congestion. The paper shows how the nested choice models can be simplified to mimic the 4-step model if that is necessary. This could be usefulto show consistency between the models and demonstrate the extra capabilities of the new model. However the full power of the activity based approach is realised when two other features are implemented: people's activities (the activity synthesiser) and micro-simulating every individual in the study area (the population synthesiser). These processes and possible migration paths are described and the relative merits of different migration sequences are discussed. Experience in migrating several models from 4-stepto activity-based models includes the Cheshire Sub Regional Strategic Transport Model, Ashford Area Transport Model and other models which were successfully migrated from 4-step models to activity based models using existing data sources. For the covering abstract see ITRD E145999
Samenvatting