Editing Trip generation (section)

===Initial analysis===
The first zonal trip generation (and its inverse, attraction) analysis in the Chicago Area Transportation Study (CATS)<ref>{{cite journal |journal=Journal of Planning Education and Research |url=https://journals.sagepub.com/doi/abs/10.1177/0739456X9001000105?journalCode=jpea |title=The Chicago Area Transportation Study: A Case Study of Rational Planning
 |first1=Alan |last1=Black |doi=10.1177/0739456X9001000105 |volume=10 |issue=1 |year=1990 | pages=27–37 | s2cid=144041009 |access-date=December 18, 2021|url-access=subscription }}</ref> followed the “decay of activity intensity with distance from the [[central business district]] (CBD)” thinking current at the time. Data from extensive surveys were arrayed and interpreted on a distance-from-CBD scale. For example, commercial land use in ring 0 (the CBD and vicinity) was found to generate 728 vehicle trips per day in 1956. That same land use in ring 5 (about {{convert|17|km|mi|abbr=on}} from the CBD) generated about 150 trips per day.

The case of trip destinations will illustrate use of the concept of activity decline with intensity (as measured by distance from CBD) worked.  Destination data are arrayed:

{| border="1" cellpadding="5" cellspacing="0" align="center"
|+'''Table: Trip Destinations per unit (Acre) of Land'''
!Ring	
!Manufacturing
!Commercial
!Open Space
!etc.
|-
| 0	
|''x''<sub>1m</sub>
|''x''<sub>1c</sub>
|''x''<sub>1os</sub>
|''x''<sub>1n</sub>
|-
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
|-
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
| <math>\vdots</math>
|-
| 7
| ''x''<sub>7m</sub>
| ''x''<sub>7c</sub>
| ''x''<sub>7os</sub>
| ''x''<sub>7n</sub>
|}               	

The land use analysis provides information on how land uses will change from an initial year (say t = 0) to some forecast year (say t = 20).  Suppose we are examining a zone.  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.  That is, there will this many acres of commercial land use, that many acres of public open space, etc., in the zone.  The acres of each use type are multiplied by the ring specific destination rates.  The result is summed to yield the zone’s trip destinations. The CATS assumed that trip destination rates would not change over time.