Trip Generation: Source: NHI Course On Travel Demand Forecasting (152054A)
Trip Generation: Source: NHI Course On Travel Demand Forecasting (152054A)
Trip Generation: Source: NHI Course On Travel Demand Forecasting (152054A)
PA Table
Typical Trip Generation Process
Demographic and Socioeconomic inputs
PA Tables,
Trip Attractions by zone, by purpose
by purpose
Balancing attractions to productions
Rule of thumb:
original
estimates of
total production
and attractions
should be
within 10% of
each other.
What is trip generation a
function of?
• Land use
• Intensity
• Location/accessibility
• Time
• Type (person, transit, auto,
walking …)
Image: www.caliper.com
aggregation
hides
variability Regression “Estimating”
a model
Y = f(X)
• Aggregate (zonal) or disaggregate (household)
• Linear or nonlinear
• Dependent (Y) variable is trips
• Independent (Xi) variables are …
– Household attributes
• E.g., population, auto ownership, income level
– Employment attributes
• E.g., number of employees or size of establishments
– Could include network attributes?
• Be careful of … co-linearity, power
• Can use your own data (best?) or borrow parameters
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Contingency tables
2007 eq.*
0-$8000
$8K-$16K
$16K-$32K
$32K-$56K
$56K plus
2007 eq.
0-$8000
$8K-$16K
$16K-$32K
$32K-$56K
$56K plus
Note: orange
lines show
how to
develop the
curves
M H
L
Now find … percent of
households in each auto
ownership/income group
“class” …
A
Given
(from
survey)
L M H
Now find … trips per
households in each
auto ownership/income
group “class” …
Given B
(from
survey)
L M H
Now find … trips by
purpose in each income
group “class” …
Given C
(from
survey)
L M H
Recall the problem …
For the zone … multiply the number of households in each income group (00)
by the percent of households owning certain number of cars by income group
(A) to get the total number of households by auto ownership in each income
group (00 x A) …see next slide series
Multiply the result (00xA) by the number of trips generated by each income
group/auto ownership category (B) to get trips by income group/auto ownership
category (00xAxB). Sum to get trips by income level (∑(00xAxB)).
Multiply this sum by the percent of trips by purpose (C) to get trips by purpose
by income group (Cx∑(00xAxB)).
Sum over all income groups to get (total trips by purpose from the zone). ANS
00
Low
x
Med
High
= 00xA
=
x
00xAxB
C
= Cx∑(00xAxB)
Cross classification model
(attractions)
Note: Less data than for productions, can use cross-class or regression,
most common classification is by type of employment
1998 Austin, TX household travel survey
Experience Based Analysis
• http://www.ite.org/tripgen/Trip_Generation
_Data_Form.pdf
Special generators