Air Transport Planning 4

Trip Distribution

Under trip distribution there is what we call the Gravity Model, which one of the so-called “synthetic” model (models based on analogies with models describing phenomena other than urban travel) used under this step.

There are several formulas that can be used under the model, upon which can be referred to many books such as Nobert Oppenheim’s “Urban travel demand modeling: from individual choices to general equilibrium”.

Modal Choice

The modal choice or the choice of transportation to be used is probably the most important question in the transportation model planning. Public transport as we know uses road space more efficiently and brings more social benefit. As we are talking about air transportation, then we would be referring to air space.

What are the factors influencing the choice of mode for transportation. The factors can be listed under three groups. The first one is the characteristic of the traveler himself with regards to his car availability or ownership, possession of a driving license, household structure, income and the residential density.

The next factors influencing mode choice based on the characteristics of the journey, which are the purpose of the undertaken trip and the time of the trip.

In terms of the models able to be used, there are basically three which are trip end modal and trip interchange modal split models. The former is used when attempts were made to apply modal-split models immediately after trip generation in responding to when personal characteristic were thought to be the most important determinants of mode choice. In this way, varying characteristics of the person could be preserved and used to estimate modal split. This traditional approach related the modal choice only to features like income, residential density and car ownership.

The next, trip-interchange generation split models is the post- distribution model, which means modal split is applied after the distribution stage. The advantage of this step is that it is possible to include the characteristics of the journey and that of the alternative modes available to undertake them.

Lastly, is the aggregate and disaggregate model which aggregates them on the basis of zonal and inter-zonal information. They can be called disaggregate if the basis upon their usage are on household and individual data.

Route Assingment

This is the fourth and last aspect of the four stage planning and involves the assigning of predicted trips to particular routes. These predicted routes could be obtained either from the trip distribution or the modal choice stage. For the former, all trips from an origin to a destination are assigned to a particular route, generally with the hypothesis that all will travel using the same mode. For those that are predicted from the modal choice, they are assigned to a more specific route. Here, bus trips will be assigned to bus routes, those driving will be assigned to road network, walking trips are assigned to a limited road network and so on. This is to say, that the assignment of travel modes is specific to a particular network.

After assigning the trips to routes, the predicted path from an origin to destination can be predicted and modeled. Apart from that, the entire trip load on road segments can be calculated.

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