Travel demand modeling is the brainchild of civil engineers and was developed to facilitate improved transportation planning. Although you can use four different approaches in travel demand modeling — trip-based, integrated trip-based, tour-based, and activity schedule-based — the trip-based approach is most relevant to crime analysis.

The trip-based approach is broken into the following four steps:

**Trip generation.**Model the*trip production*(the quantity of crime trips that originate in a*zone of origination*— a spatial region, like a neighborhood or subdivision) and the*trip attractions*(the quantity of crime trips that end in the*zone of destination*— the spatial region where the criminal act is executed).**Trip distribution.**Incorporate a*trip matrix*— a matrix of rows and columns that covers a study area and depicts the patterns of trips across it— and a*gravity model*— a model that describes and predicts the locational flow of objects across space — to quantify the count of crime trips that occur between each zone of origination and each zone of destination.**Modal split.**A*modal split*is the portion of travelers that uses particular trip paths across a study area. For travel demand modeling, you'd generate a count of the number of trips for each zone-of-origination/zone-of-destination pair that occurs via each available route. The choice between routes can be modeled statistical or mathematical.**Network assignment.**Assign probability and predict the most likely routes that a criminal would take when traveling from a particular zone of origination to a particular zone of destination across the network of potential travel paths.