At the level of the traffic analysis zone, residential land uses "produce" or generate trips.
The first zonal trip generation (and its inverse, attraction) analysis in the Chicago Area Transportation Study (CATS)[2] followed the “decay of activity intensity with distance from the central business district (CBD)” thinking current at the time.
For example, commercial land use in ring 0 (the CBD and vicinity) was found to generate 728 vehicle trips per day in 1956.
The case of trip destinations will illustrate use of the concept of activity decline with intensity (as measured by distance from CBD) worked.
We take the mix of land uses projected, say, for year t = 20 and apply the trip destination rates for the ring in which the zone is located.
As was true for land use analysis, the approach developed at CATS was considerably modified in later studies.
Person, transit, walking, and auto trips per unit of time are regressed on variables thought to be explanatory, such as: household size, number of workers in the household, persons in an age group, type of residence (single family, apartment, etc.
In other cases, regressions, usually of the form trip rate = f(number of employees, floor area of establishment), are made for land use types.
Ongoing work is adding to the stockpile of numbers; over 4000 studies were aggregated for the latest edition.
ITE Procedures estimate the number of trips entering and exiting a site at a given time.
ITE Rates are functions of type of development based on independent variables such as square footage of the gross leasable area, number of gas pumps, number of dwelling units, or other standard measurable things, usually produced in site plans.
Many localities require their use to ensure adequate public facilities for growth management and subdivision approval.
In the United Kingdom and Ireland, the TRICS database is commonly used to calculate trip generation.