Trip Generation
Trip generation is the first step in the traditional four-step transportation forecasting
process, widely used for forecasting travel demands. Trip generation is the process of estimating
the number of trips that will begin or end in each traffic analysis zone. Trip Generation have two
functions:


To develop a relationship between trip end production or attraction and land use
To use the relationship to estimate the number of trips generated at some future date
under a new set of land use conditions
The trip rates data that are used for trip generation models can be characterized by Trip Makers
(Age, income, auto ownership & household size) and Development (Units & Area).
Methods of Creating a Trip Generation Model
There are two methods making a trip generation model. These methods are:

Trip rates based on Activity Unit
Trips generated at the household end are referred to as productions, and they are attracted
to zones for purposes such as work, shopping, visiting friends, and medical trips. In this
method measures like square feet of floor space or the number of employees might be used to
characterize an activity unit.
Example 1
A commercial center in the downtown contains several retail establishments and light
industries. Employed at the center are 220 retail and 650 non-retail workers. Determine the
number of trips per day attracted to this zone.

Cross-Classification
Developed by Federal Highway Administration (FHWA) to determine the number of
trips that begin and end at the home. This method is a more specific and complex version of
simple rate models. Classification of data can be based upon income, vehicle ownership,
household size and trip purpose.
Example 2:
Examine the following data:
Example 3:
Consider a zone that is located in a suburban area of a city. The population and income
data for the zone are as follows.
Number of dwelling units: 60
Average income per dwelling unit: $44,000
Determine the number of trips per day generated in this zone for each trip purpose,
assuming that the characteristics depicted in the previous example apply in this situation.
The problem is solved in four basic steps.
Balancing Productions and Attractions
Productions are trips that begin in a zone, while attractions are trips that end in a zone. A
likely result of the trip generation process is that the number of trip productions may not be equal
to the number of trip attractions. Trip productions, which are based on census data, are
considered to be more accurate than trip attractions. With this particular reason, we scale the rate
of attractions to match the number of total productions.
REFERENCES
Garber, N. J., & Hoel, L. A. (2008). Traffic & Highway Engineering, 4th Edition (4th ed.).
Cengage Learning.