Four Step Travel Demand Model

Travel demand modeling

Travel demand modeling aims to establish the spatial distribution of travel utilizing an appropriate system of zones. Modeling of demand is a procedure for predicting what travel decisions people would like to make taking consideration of the generalized travel cost of each alternative. ( The generalized cost is the sum of the monetary and non-monetary costs of a journey.) 

The basic decisions making include the choice of destination, the choice of the mode, and the choice of the route. There are various modeling approaches are adopted, but in this blog, we will discuss only popularly known model “four-stage travel demand model” (FSM).The general form of the four-stage model is as follows,

                                    

                Figure: General form of the four-stage modeling

   

This model presents a sequence of four sub-models: trip generation, trip distribution, modal split, trip assignment. The models start with defining the study area and dividing them into several zones and considering all the transport networks in the system. Then the trip generation model uses the necessary data to estimate the total number of trips generated and attracted by each zone. The next step is the allocation of these trips from each zone to various other destination zones in the study area using trip distribution models. The output of the above model is an origin-destination trip matrix (O-D Matrix) which denotes the trips from each zone to every other zones. In the succeeding step, the trips are allocated to different modes based on the modal attributes using the modal split models. This is essentially de-categorizing the trip matrix for various modes generated to a mode-specific trip matrix. Finally, each trip matrix is assigned to the route network of that particular mode using the trip assignment models. The step will give the assigned traffic on each link of the network.

This model also answered a series of questions namely how many trips are generated, where they are going, what mode they are using, and finally which route they are adopting for their travel. 

For detail understanding you can refer the NPTEL video by clicking the given link https://youtu.be/kjsvNenr0Jg