Travel Demand Modeling comprises a vast spectrum of topics as a part of regional transportation planning. It is performed to help the decision-makers to take proper transportation planning decisions.
The following four-step process is being used for regional transportation planning analysis.
1. Trip generation – Used to estimate the total number of trips generated in each area.
2. Trip distribution – Used to calculate the number of trips from one zone to other zones.
3. Mode choice – Used to identify the mode of transportation
4. Trip assignment – Used to predict the route trips made by the vehicles.
Trip Generation Model or Regression Model is the first step of the four steps of transportation planning. This model predicts the total number of trips generated in a particular traffic analysis zone (TAZ). It focuses on residences and the trips generated from residences are a function of the social and economic attributes of households.
The Gravity Model or Trip Distribution Model or Destination Choice Model or Zonal Interchange Analysis is the second step in the travel modeling after the trip generation but before modal choice and trip assignment. Through this model trip maker’s origin and destination are matched to form a ’trip table’. The trip table is a matrix that shows the number of trips made from each origin to the destination.
The Mode Choice or Modal Share or Modal Split or Mode Share or Mode Split is the percentage of people using a certain type of transport or the number of trips made by a certain vehicle. It may be measured in mass, in the case of freight transportation.
Modal Split is an essential part of developing a sustainable transport system within the city or town. At present, several cities have set mode share targets for sustainable and balanced transport systems, particularly 30% public transport and another 30% of non-motorized transport, viz., cycling or walking. This shows a desire for mode choice or a change between modes, and eventually increasing the proportion of trips made with sustainable modes of transport.
Trip Assignment or Minimum Tree Search Model assigns traffic to a certain transportation network like roads or streets. Using a mathematical algorithm, traffic is assigned to the transit or roadway routes. This determines the traffic amount as a function of volume, time, impedance factor, or capacity. This model helps to find the routes travelers would be taking from origin to destination.
Once all these four methods are done, the model provides the planner with a picture of existing travel patterns. The results obtained are then given a reality check. The results obtained from the travel demand modeling help the decision-makers to form a proper transportation planning decision. However, the results we get from these models vary depending upon the information and the ideas used, and the sophistication and accuracy of the particular model.